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#1
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Questions on Levels
Dear Audio Professionals,
Questions on levels: 1. If you backtrack to 0 dB from this wikipedia article http://en.wikipedia.org/wiki/Line_level the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS, respectively. Is this correct? Are the reference levels I've given here exact? 2. Is there a standard for converting from dBFS to dBu? If so, what is it? 3. If the answer to 2 is yes, then does that standard use FS sine or FS square? Thanks for any insights. -- Randy Yates % "Maybe one day I'll feel her cold embrace, Digital Signal Labs % and kiss her interface, % til then, I'll leave her alone." http://www.digitalsignallabs.com % 'Yours Truly, 2095', *Time*, ELO |
#2
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
cross-posting to rec.audio.pro
--RY Randy Yates writes: Dear Audio Professionals, Questions on levels: 1. If you backtrack to 0 dB from this wikipedia article http://en.wikipedia.org/wiki/Line_level the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS, respectively. Is this correct? Are the reference levels I've given here exact? 2. Is there a standard for converting from dBFS to dBu? If so, what is it? 3. If the answer to 2 is yes, then does that standard use FS sine or FS square? Thanks for any insights. -- Randy Yates % "And all that I can do Digital Signal Labs % is say I'm sorry, % that's the way it goes..." http://www.digitalsignallabs.com % Getting To The Point', *Balance of Power*, ELO |
#3
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
One other question: is there a specification on the absolute maximum
signal voltage magnitude for a line level output? --RY Randy Yates writes: cross-posting to rec.audio.pro --RY Randy Yates writes: Dear Audio Professionals, Questions on levels: 1. If you backtrack to 0 dB from this wikipedia article http://en.wikipedia.org/wiki/Line_level the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS, respectively. Is this correct? Are the reference levels I've given here exact? 2. Is there a standard for converting from dBFS to dBu? If so, what is it? 3. If the answer to 2 is yes, then does that standard use FS sine or FS square? Thanks for any insights. -- Randy Yates % "With time with what you've learned, Digital Signal Labs % they'll kiss the ground you walk % upon." http://www.digitalsignallabs.com % '21st Century Man', *Time*, ELO |
#4
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
Randy Yates wrote:
One other question: is there a specification on the absolute maximum signal voltage magnitude for a line level output? Most preamps will put out close to 10 VRMS, considering the typical +/- 15V power-supply rails... |
#5
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
On Nov 18, 8:39*pm, Randy Yates wrote:
* 1. If you backtrack to 0 dB from this wikipedia article * *http://en.wikipedia.org/wiki/Line_level * the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS, * respectively. Is this correct? Are the reference levels I've given * here exact? No and yes, respectively. The reference level for dBu is actually 0.77459666924148337703585307995648V, according to my calculator -- that's the voltage equivalent of 1mW into a 600 ohm load. The reference level for dBV is exactly 1V. * 2. Is there a standard for converting from dBFS to dBu? If so, * what is it? No. There's an informal standard used in the film industry and in many broadcast applications of +4dBu = -20dBFS, but it's never been codified as an official standard. The informal standard, though, is (I believe) based on an rms scale -- in other words, a tone that would read 0 VU on a VU meter calibrated to +4dBu would be -20dBFS. Correct me if I'm wrong on that last bit, but that's what I think is the case. Peace, Paul |
#6
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
Randy Yates wrote:
One other question: is there a specification on the absolute maximum signal voltage magnitude for a line level output? No. I've seen some that clip at +30dBu. Peace, Paul |
#7
Posted to rec.audio.tech
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Questions on Levels
On Thu, 18 Nov 2010 21:19:50 -0500, Randy Yates
wrote: Dear Audio Professionals, Questions on levels: 1. If you backtrack to 0 dB from this wikipedia article http://en.wikipedia.org/wiki/Line_level the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS, respectively. Is this correct? Are the reference levels I've given here exact? 2. Is there a standard for converting from dBFS to dBu? If so, what is it? 3. If the answer to 2 is yes, then does that standard use FS sine or FS square? Thanks for any insights. I'm a little confused. You work in a signals lab - I would be recommending you ask yourself. Anyway, Q1. 0dBu is the voltage level that would have produced 1mW in a 600 ohm system (0dBm). so it is sqrt(600 * .001), or sqrt (0.6), which is as you say 0.775 volts. Q2. No. FS is what you make it. It is a peak measurement, not an RMS one, so there is no direct correlation between dBu and dBFS for a musical waveform. You can get somewhere near it by specifying a given crest factor but that is still at best an approximation. The best you can probably do is to specify in terms of the peak/RMS (root 2) of a sine wave. The square wave case is very artificial, and results in an apparent ability to fit an oversized sine component into a smaller space, but this is strictly for the square case, and can be ignored for practical purposes. d |
#8
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
PStamler wrote:
On Nov 18, 8:39*pm, Randy Yates wrote: * 1. If you backtrack to 0 dB from this wikipedia article * *http://en.wikipedia.org/wiki/Line_level * the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS, * respectively. Is this correct? Are the reference levels I've given * here exact? No and yes, respectively. The reference level for dBu is actually 0.77459666924148337703585307995648V, according to my calculator -- that's the voltage equivalent of 1mW into a 600 ohm load. The reference level for dBV is exactly 1V. * 2. Is there a standard for converting from dBFS to dBu? If so, * what is it? No. There's an informal standard used in the film industry and in many broadcast applications of +4dBu = -20dBFS, but it's never been codified as an official standard. The informal standard, though, is (I believe) based on an rms scale -- in other words, a tone that would read 0 VU on a VU meter calibrated to +4dBu would be -20dBFS. Correct me if I'm wrong on that last bit, but that's what I think is the case. The optimum reference headroom (the difference between reference level and full-scale level) would vary according to the application and the equipment used. With lots of bits to spare, 20dB would be fine, but if you were recording to 16-bit CD standards, you would have thrown away 20dB of your potential dynamic range and dropped your signal/noise ratio to around 45 dB for average levels. (Digital noise sounds horrible, much worse than analogue noise, so you really do want to keep clear of it.) For something like A.M. broadcasting, a reference headroom of around 12 dB is more common and that is also quite satisfactory for 16-bit recordings provided you are prepared to control the gain intelligently on the very loudest passages. If part of the chain is in mono, there is the further complication that two stereo channels can add to give any level from much lower to 6dB higher, depending on coherence and phase. For professional use, the system of marking the beginning of a recording with a burst of reference tone (or a series of squeaks if equalisation is involved) is the simplest way of ensuring the correct playback or copying level. -- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk |
#9
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
"dizzy" wrote in message
Randy Yates wrote: One other question: is there a specification on the absolute maximum signal voltage magnitude for a line level output? Most preamps will put out close to 10 VRMS, considering the typical +/- 15V power-supply rails... One word: tubes. |
#10
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
On Nov 18, 9:39*pm, Randy Yates wrote:
* the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS, * respectively. Is this correct? Are the reference levels I've given * here exact? Exact for dBV, close enough for engineering purposes for dBu. * 2. Is there a standard for converting from dBFS to dBu? No. This is a great point of confusion. You can't directly convert them because they describe different kinds of units. It's like converting the number of apples in a bushel to the number of potatoes in a bushel. There are a few conventions, however, but mostly there's things that you choose for yourself, not a standard to which a manufacturer adheres. Back when people had VU meters and digital recorders had readable meter scales and an adjustable input level control, there was often a mark typically somewhere between -16 and -20 dBFS on the digital meter that was the recommended point corresponding to 0 VU. But it's rare to see that any more. If you're working with 24-bit converters and material with fairly high dynamic range, I'd recommend 0 VU (at whatever level that represents) provides a record level of -20 dBFS. But it's up to you. One other question: is there a specification on the absolute maximum signal voltage magnitude for a line level output? No specification or standard, but since most gear you'll find today operates from a +/- 15 volt power supply, it's rare to find a maximum output level before clipping much higher than +24 dBu. There are exceptions, of course. You'll find some discussion of these issues in the Gozintas and Gozoutas and Meter Madness articles in the Technical Articles section of my web site. http://mikeriversaudio.wordpress.com |
#11
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
Hi Paul,
Thank you for your answers. Comments below. PStamler writes: On Nov 18, 8:39Â*pm, Randy Yates wrote: Â* 1. If you backtrack to 0 dB from this wikipedia article Â* Â*http://en.wikipedia.org/wiki/Line_level Â* the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS, Â* respectively. Is this correct? Are the reference levels I've given Â* here exact? No and yes, respectively. The reference level for dBu is actually 0.77459666924148337703585307995648V, according to my calculator -- that's the voltage equivalent of 1mW into a 600 ohm load. Ah, that's right - it's the voltage level that corresponds to 0 dBm (1 mW) when delivering to a 600 ohm load. The reference level for dBV is exactly 1V. Got it. Â* 2. Is there a standard for converting from dBFS to dBu? If so, Â* what is it? No. There's an informal standard used in the film industry and in many broadcast applications of +4dBu = -20dBFS, but it's never been codified as an official standard. The informal standard, though, is (I believe) based on an rms scale -- in other words, a tone that would read 0 VU on a VU meter calibrated to +4dBu would be -20dBFS. Correct me if I'm wrong on that last bit, but that's what I think is the case. There seems to be no universal agreement, but you are close to what this guy says (under "Here come the numbers..."): +22dBu = 0dBFS == +4dBu = -18dBFS. I'm still not sure if that's FS sine or FS square. -- Randy Yates % "Remember the good old 1980's, when Digital Signal Labs % things were so uncomplicated?" % 'Ticket To The Moon' http://www.digitalsignallabs.com % *Time*, Electric Light Orchestra |
#12
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
Mike Rivers writes:
On Nov 18, 9:39Â*pm, Randy Yates wrote: Â* the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS, Â* respectively. Is this correct? Are the reference levels I've given Â* here exact? Exact for dBV, close enough for engineering purposes for dBu. Right. As Paul said, dBu reference is the voltage corresponding to 1 mW into 600 ohms. I knew this - just temporarily forgot (). Â* 2. Is there a standard for converting from dBFS to dBu? No. This is a great point of confusion. You can't directly convert them because they describe different kinds of units. It's like converting the number of apples in a bushel to the number of potatoes in a bushel. Well, yeah, I didn't mean that way. What I meant to ask is if there is a standard way to map the full-scale output of a DAC (or input of an ADC) to a specific voltage voltage level. There are a few conventions, however, but mostly there's things that you choose for yourself, not a standard to which a manufacturer adheres. Back when people had VU meters and digital recorders had readable meter scales and an adjustable input level control, there was often a mark typically somewhere between -16 and -20 dBFS on the digital meter that was the recommended point corresponding to 0 VU. And 0 VU correspondings to +4dBu? But it's rare to see that any more. If you're working with 24-bit converters and material with fairly high dynamic range, I'd recommend 0 VU (at whatever level that represents) provides a record level of -20 dBFS. But it's up to you. That's the same translation Paul mentioned: +4dBu = -20 dBFS. No one has yet answered the question about whether it's FS sine or FS square. One other question: is there a specification on the absolute maximum signal voltage magnitude for a line level output? No specification or standard, but since most gear you'll find today operates from a +/- 15 volt power supply, it's rare to find a maximum output level before clipping much higher than +24 dBu. There are exceptions, of course. Thank you, Mike. You'll find some discussion of these issues in the Gozintas and Gozoutas and Meter Madness articles in the Technical Articles section of my web site. http://mikeriversaudio.wordpress.com OK, great. Thanks for the pointers, Mike. -- Randy Yates % "Midnight, on the water... Digital Signal Labs % I saw... the ocean's daughter." % 'Can't Get It Out Of My Head' http://www.digitalsignallabs.com % *El Dorado*, Electric Light Orchestra |
#13
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
On 11/19/2010 10:01 AM, Randy Yates wrote:
+22dBu = 0dBFS == +4dBu = -18dBFS. I'm still not sure if that's FS sine or FS square. dBFS is a peak level. But since good peak reading meters (and good average reading meters as well) are pretty rare, generally we look at the RMS value of a sine wave when expressing levels. I determine the maximum input level experimentally by feeding in a sine wave, watching the digital meter, and looking at the RMS value of the sine wave when the overload light just comes on. To be more accurate, I'll record a bit and examine the level for clipping, boosting the input level incrementally until I'm sure I'm reaching full scale on peaks. For outputs, I'll use a program to generate a 0 dBFS sine wave, play it, and read the RMS level of the output. -- "Today's production equipment is IT based and cannot be operated without a passing knowledge of computing, although it seems that it can be operated without a passing knowledge of audio." - John Watkinson http://mikeriversaudio.wordpress.com - useful and interesting audio stuff |
#14
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
Mike Rivers writes:
On 11/19/2010 10:01 AM, Randy Yates wrote: +22dBu = 0dBFS == +4dBu = -18dBFS. I'm still not sure if that's FS sine or FS square. dBFS is a peak level. That's not the way I understand it. Am I wrong? It's no different than dBu or dBV - just a different "reference" level. Thus it would be an RMS measure. But since good peak reading meters (and good average reading meters as well) are pretty rare, generally we look at the RMS value of a sine wave when expressing levels. So you're saying then it's FS sine. -- Randy Yates % "Maybe one day I'll feel her cold embrace, Digital Signal Labs % and kiss her interface, % til then, I'll leave her alone." http://www.digitalsignallabs.com % 'Yours Truly, 2095', *Time*, ELO |
#15
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
In article , Randy Yates wrote:
One other question: is there a specification on the absolute maximum signal voltage magnitude for a line level output? No, and that's the problem. The standards are average and not peak standards, and so the amount of headroom required over average is not defined. For me, I'd like to see 20 dB over average level before clipping, maybe more. Unfortunately a lot of "pro audio" gear does not do this. I believe your questions are answered by IEC 60027-3, and by AES standard AES-R2-1998. Peak-reading standards are in AES-R7-2006. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#16
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
PStamler wrote:
On Nov 18, 8:39=A0pm, Randy Yates wrote: =A0 1. If you backtrack to 0 dB from this wikipedia article =A0 =A0http://en.wikipedia.org/wiki/Line_level =A0 the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS, =A0 respectively. Is this correct? Are the reference levels I've given =A0 here exact? No and yes, respectively. The reference level for dBu is actually 0.77459666924148337703585307995648V, according to my calculator -- that's the voltage equivalent of 1mW into a 600 ohm load. The reference level for dBV is exactly 1V. =A0 2. Is there a standard for converting from dBFS to dBu? If so, =A0 = what is it? No. There's an informal standard used in the film industry and in many broadcast applications of +4dBu =3D -20dBFS, but it's never been codified as an official standard. The informal standard, though, is (I believe) based on an rms scale -- in other words, a tone that would read 0 VU on a VU meter calibrated to +4dBu would be -20dBFS. Correct me if I'm wrong on that last bit, but that's what I think is the case. This is sort of like asking if there is a standard for converting pounds to feet. They aren't measuring the same thing. If you know something specific about the item being measured, you can make some good estimates, but you need to know something more. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#17
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
In article , Randy Yates wrote:
No. There's an informal standard used in the film industry and in many broadcast applications of +4dBu = -20dBFS, but it's never been codified as an official standard. The informal standard, though, is (I believe) based on an rms scale -- in other words, a tone that would read 0 VU on a VU meter calibrated to +4dBu would be -20dBFS. Correct me if I'm wrong on that last bit, but that's what I think is the case. There seems to be no universal agreement, but you are close to what this guy says (under "Here come the numbers..."): +22dBu = 0dBFS == +4dBu = -18dBFS. I'm still not sure if that's FS sine or FS square. That's assuming a sine wave. Unfortunately if you use that standard and you record a trumpet with peaks at 0 dBu, you'll clip the hell out of your converters. This is because trumpets aren't making sine waves. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#18
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
On Nov 19, 8:29*am, (Scott Dorsey) wrote:
In article , Randy Yates wrote: One other question: is there a specification on the absolute maximum signal voltage magnitude for a line level output? No, and that's the problem. *The standards are average and not peak standards, and so the amount of headroom required over average is not defined. * For me, I'd like to see 20 dB over average level before clipping, maybe more. Unfortunately a lot of "pro audio" gear does not do this. I believe your questions are answered by IEC 60027-3, and by AES standard AES-R2-1998. *Peak-reading standards are in AES-R7-2006. --scott The nice thing about standards is that there are so many of them. I have posted a JPEG scan of a level scales card I picked up some time ago a convention. It shows the relationship of 0.775Vrms to most known standard scales. See: http://www.klay.com/klay/world_audio_levels.jpg Text "Klay" to 50500 for contact info -.- .-.. .- -.-- / .- - / -.- .-.. .- -.-- / -.. --- - / -.-. --- -- Yours truly, Mr. Klay Anderson, D.A.,Q.B.E. |
#19
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
On Nov 19, 7:41*am, "Arny Krueger" wrote:
"dizzy" wrote in message Randy Yates wrote: One other question: is there a specification on the absolute maximum signal voltage magnitude for a line level output? Most preamps will put out close to 10 VRMS, considering the typical +/- 15V power-supply rails... One word: tubes. And two more words: differential outputs. With higher supply voltages (like +/- 21V) there are several common opamps which will (just) put out +24dBu. Use a pair of them as a differential output and you get +30dBu max output. Or you can use a higher-supply-voltage discrete circuit or, as Arny says, tubes. Peace, Paul |
#21
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
On 11/19/2010 7:45 AM Scott Dorsey spake thus:
In article , Randy Yates wrote: No. There's an informal standard used in the film industry and in many broadcast applications of +4dBu = -20dBFS, but it's never been codified as an official standard. The informal standard, though, is (I believe) based on an rms scale -- in other words, a tone that would read 0 VU on a VU meter calibrated to +4dBu would be -20dBFS. Correct me if I'm wrong on that last bit, but that's what I think is the case. There seems to be no universal agreement, but you are close to what this guy says (under "Here come the numbers..."): +22dBu = 0dBFS == +4dBu = -18dBFS. I'm still not sure if that's FS sine or FS square. That's assuming a sine wave. Unfortunately if you use that standard and you record a trumpet with peaks at 0 dBu, you'll clip the hell out of your converters. This is because trumpets aren't making sine waves. Nor violins. (Make pretty close to a triangular wave, I believe.) -- The fashion in killing has an insouciant, flirty style this spring, with the flaunting of well-defined muscle, wrapped in flags. - Comment from an article on Antiwar.com (http://antiwar.com) |
#22
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
On 11/19/2010 10:09 AM, Randy Yates wrote:
What I meant to ask is if there is a standard way to map the full-scale output of a DAC (or input of an ADC) to a specific voltage voltage level. Nope. There are a few conventions, however, but mostly there's things that you choose for yourself, not a standard to which a manufacturer adheres. Back when people had VU meters and digital recorders had readable meter scales and an adjustable input level control, there was often a mark typically somewhere between -16 and -20 dBFS on the digital meter that was the recommended point corresponding to 0 VU. And 0 VU correspondings to +4dBu? Another point of great confusion. 0 VU is whatever nominal operating level is. On "pro" equipment, it's usually +4 dBu. On "semi-pro" equipment, it's usually -10 dBV. On some phone company, it's +8 dBm (a unit of power, not voltage, but usually into 600 ohms, so you can calculate the voltage). On a consumer tape deck, who the heck knows? Usually somewhere around -20 dBu. That's the same translation Paul mentioned: +4dBu = -20 dBFS. Yup, he's a smart feller. No one has yet answered the question about whether it's FS sine or FS square. It doesn't really matter until you want to find the RMS value of the waveform that got you to that digital level. If 0dBFS = +24 dBu, either a square wave or a sine wave with the same peak value will get you there. The RMS value of a sine wave is 0.707 (1/2 the square root of 2) times the peak amplitude. The RMS value of a square wave is the same as the peak amplitude. -- "Today's production equipment is IT based and cannot be operated without a passing knowledge of computing, although it seems that it can be operated without a passing knowledge of audio." - John Watkinson http://mikeriversaudio.wordpress.com - useful and interesting audio stuff |
#23
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
On 11/19/2010 10:22 AM, Randy Yates wrote:
Mike writes: dBFS is a peak level. That's not the way I understand it. Am I wrong? It's no different than dBu or dBV - just a different "reference" level. Thus it would be an RMS measure. We're getting wrapped around the axle here since I don't know what your real question is. What you're asking is kind of abstract. dBFS is dB referenced to full scale which is all the bits on dBu is dB referenced to .775 volts dBV is dB referenced to 1 volt Any of those can be RMS or peak. Peak is significant when dealing with digital levels, but the only level that's really significant is the one beyond which you can't go higher, and that's only one level, 0 dBFS So you're saying then it's FS sine. If you say so. Please ask your REAL question if you have one. Are you looking for a solution to a problem? Or trying to interpret some marketing goof's data sheet or manual? If you're just looking for definitions and conventions, then you have them. -- "Today's production equipment is IT based and cannot be operated without a passing knowledge of computing, although it seems that it can be operated without a passing knowledge of audio." - John Watkinson http://mikeriversaudio.wordpress.com - useful and interesting audio stuff |
#24
Posted to rec.audio.tech,rec.audio.pro,comp.dsp
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Questions on Levels
Mike Rivers writes:
On 11/19/2010 10:22 AM, Randy Yates wrote: Mike writes: dBFS is a peak level. That's not the way I understand it. Am I wrong? It's no different than dBu or dBV - just a different "reference" level. Thus it would be an RMS measure. We're getting wrapped around the axle here since I don't know what your real question is. What you're asking is kind of abstract. Is dBFS abstract? If so, then I guess I'm asking an abstract question. My question is this: What is the definition of dBFS? dBFS is dB referenced to full scale which is all the bits on dBu is dB referenced to .775 volts dBV is dB referenced to 1 volt Any of those can be RMS or peak. Peak is significant when dealing with digital levels, but the only level that's really significant is the one beyond which you can't go higher, and that's only one level, 0 dBFS If dBFS is defined as dBFS = 20 * log_10(XRMS / (RMS value of full-scale sine wave), where XRMS is the RMS value of the digital data stream, and you're generating a "digital square wave," then you are wrong. The digital square wave can go to +3dBFS as defined above. So you're saying then it's FS sine. If you say so. Please ask your REAL question if you have one. Are you looking for a solution to a problem? Or trying to interpret some marketing goof's data sheet or manual? If you're just looking for definitions and conventions, then you have them. It seems that there really is no standard definition. That's the problem. It's not a matter of abstractness, but rather of well-definedness. -- Randy Yates % "She's sweet on Wagner-I think she'd die for Beethoven. Digital Signal Labs % She love the way Puccini lays down a tune, and % Verdi's always creepin' from her room." http://www.digitalsignallabs.com % "Rockaria", *A New World Record*, ELO |
#25
Posted to rec.audio.tech,rec.audio.pro
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Questions on Levels
"Randy Yates" wrote in message ... Hi Paul, Thank you for your answers. Comments below. PStamler writes: On Nov 18, 8:39 pm, Randy Yates wrote: 1. If you backtrack to 0 dB from this wikipedia article http://en.wikipedia.org/wiki/Line_level the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS, respectively. Is this correct? Are the reference levels I've given here exact? No and yes, respectively. The reference level for dBu is actually 0.77459666924148337703585307995648V, according to my calculator -- Wow! You have a calculator that goes to 32 significant digits? My old HP15C is only good for about 15. You can calculate the distance to Alpha Centauri to the nearest tenth of an inch...:^) |
#26
Posted to rec.audio.tech,rec.audio.pro,comp.dsp
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Questions on Levels
On 11/19/2010 7:52 PM, Randy Yates wrote:
My question is this: What is the definition of dBFS? Decibels relative to full scale. 0 dBFS is full scale, everything else is down from there. -6 dBFS is half the maximum number as with all the bits on. If dBFS is defined as dBFS = 20 * log_10(XRMS / (RMS value of full-scale sine wave), where XRMS is the RMS value of the digital data stream, and you're generating a "digital square wave," then you are wrong. The digital square wave can go to +3dBFS as defined above. But it's not defined that way. In reality, you can't have anything higher than 0 dBFS. That's where you run out of numbers to express the amplitude. There's such a thing as "intersample overload" where the input actually goes higher than the 0 dBFS level between two adjacent samples, but that's an anomaly. It seems that there really is no standard definition. That's the problem. It's not a matter of abstractness, but rather of well-definedness. The thing is that what you're concerned with in digital recording is how much headroom you have. You can choose your own headroom amount simply by choosing the analog reference level that gives your desired headroom. If you're compressing the **** out of everything, you don't need as much headroom as if you're recording an orchestra or something where you're unsure of the input dynamic range, and you can choose a higher reference level. For most music, 20 dB of headroom is pretty safe, which is why the -20 dBFS reference is fairly common. -- "Today's production equipment is IT based and cannot be operated without a passing knowledge of computing, although it seems that it can be operated without a passing knowledge of audio." - John Watkinson http://mikeriversaudio.wordpress.com - useful and interesting audio stuff |
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Questions on Levels
Mike Rivers writes:
On 11/19/2010 7:52 PM, Randy Yates wrote: My question is this: What is the definition of dBFS? Decibels relative to full scale. Nonsense. All you've given is the meaning of the acronym, not an engineering definition of the unit. This is similar to stating the definition of RMS is "root mean square." [...] But it's not defined that way. I'm not asking how it's not defined. I'm asking how it is defined (in a sensible way). -- Randy Yates % "And all that I can do Digital Signal Labs % is say I'm sorry, % that's the way it goes..." http://www.digitalsignallabs.com % Getting To The Point', *Balance of Power*, ELO |
#28
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Questions on Levels
Randy Yates wrote:
Is dBFS abstract? In the sense that it correlates to no specific power or voltage level in the analog world, yes. When we include information about the converter's input expectations then we can link these disparate measurements. If so, then I guess I'm asking an abstract question. I don't think that's the case. There are concrete answers to your question(s), even if they wrap an abstract concept. My question is this: What is the definition of dBFS? Theorectically, when the last bit of dynamic range is utilized, that will be shown by the metering as 0 dBFS. Any increase of input level thereafter will result in clipping. -- shut up and play your guitar * http://hankalrich.com/ http://armadillomusicproductions.com/who'slistening.html http://www.sonicbids.com/HankandShai...withDougHarman |
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Questions on Levels
Randy Yates wrote:
Mike Rivers writes: On 11/19/2010 7:52 PM, Randy Yates wrote: My question is this: What is the definition of dBFS? Decibels relative to full scale. Nonsense. All you've given is the meaning of the acronym, not an engineering definition of the unit. This is similar to stating the definition of RMS is "root mean square." Nope. It is exactly what Mike stated. It's the "that's all there is and there ain't no more" point in the converter, assuming heh that the metering and the conveter's actual performance are accurately linked. -- shut up and play your guitar * http://hankalrich.com/ http://armadillomusicproductions.com/who'slistening.html http://www.sonicbids.com/HankandShai...withDougHarman |
#30
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Questions on Levels
In article , Randy Yates wrote:
If dBFS is defined as dBFS = 20 * log_10(XRMS / (RMS value of full-scale sine wave), where XRMS is the RMS value of the digital data stream, and you're generating a "digital square wave," then you are wrong. The digital square wave can go to +3dBFS as defined above. dBFS has not got a damn thing to do with sine waves or reference levels or anything in the analogue world. It has ONLY to do with how far a digital level is below the point at which the digital value reaches full scale (all bits on). --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#31
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Questions on Levels
(Scott Dorsey) writes:
In article , Randy Yates wrote: If dBFS is defined as dBFS = 20 * log_10(XRMS / (RMS value of full-scale sine wave), where XRMS is the RMS value of the digital data stream, and you're generating a "digital square wave," then you are wrong. The digital square wave can go to +3dBFS as defined above. dBFS has not got a damn thing to do with sine waves or reference levels or anything in the analogue world. Again, I'm not asking how it's not defined, I'm asking how it is defined. You guys have danced around this one all day. It's getting humorous. It has ONLY to do with how far a digital level is below the point at which the digital value reaches full scale (all bits on). If you know what it means, and you're literate, then you should be able to come up with a precise definition. I haven't seen one yet. -- Randy Yates % "She has an IQ of 1001, she has a jumpsuit Digital Signal Labs % on, and she's also a telephone." % http://www.digitalsignallabs.com % 'Yours Truly, 2095', *Time*, ELO |
#32
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Questions on Levels
On Nov 20, 2:46*am, Randy Yates wrote:
(Scott Dorsey) writes: In article , Randy Yates wrote: If dBFS is defined as *dBFS = 20 * log_10(XRMS / (RMS value of full-scale sine wave), where XRMS is the RMS value of the digital data stream, and you're generating a "digital square wave," then you are wrong. The digital square wave can go to +3dBFS as defined above. dBFS has not got a damn thing to do with sine waves or reference levels or anything in the analogue world. Again, I'm not asking how it's not defined, I'm asking how it is defined. You guys have danced around this one all day. It's getting humorous. It has ONLY to do with how far a digital level is below the point at which the digital value reaches full scale (all bits on). If you know what it means, and you're literate, then you should be able to come up with a precise definition. I haven't seen one yet. -- Randy Yates * * * * * * * * * * *% "She has an IQ of 1001, she has a jumpsuit Digital Signal Labs * * * * * * *% * * * * * *on, and she's also a telephone." * * * * *%http://www.digitalsignallabs.com% * * * *'Yours Truly, 2095', *Time*, ELO * ratio (dBFS) = 20log10 (magnitude / maximum possible or allowable magnitude). How you measure/define magnitude is the interesting question. i.e. peak, rms, average, whatever |
#33
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Questions on Levels
On Fri, 19 Nov 2010 20:32:08 -0500, Randy Yates
wrote: Mike Rivers writes: On 11/19/2010 7:52 PM, Randy Yates wrote: My question is this: What is the definition of dBFS? Decibels relative to full scale. Nonsense. All you've given is the meaning of the acronym, not an engineering definition of the unit. This is similar to stating the definition of RMS is "root mean square." [...] But it's not defined that way. I'm not asking how it's not defined. I'm asking how it is defined (in a sensible way). I think you're asking what color the sky is, and people are telling you "blue", but you're expecting a wavelength or something, so you're not accepting the answer. As you know, dB measurements are always relative to some reference level. With dBFS the reference level is Full Scale of the converter or number system or whatever. The ratio of the level measured to the Full Scale level provides the argument for the logarithm, and the scaled result is dBFS. If you can do dBm, or dBW, or dBC, you should be able to do dBFS. The odd part is that you're not seeing this after being told correctly what it is several times. Eric Jacobsen Minister of Algorithms Abineau Communications http://www.abineau.com |
#34
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Questions on Levels
(Eric Jacobsen) writes:
The ratio of the level measured to the Full Scale level provides the argument for the logarithm, and the scaled result is dBFS. "the level measured"? I can immediately think of three different ways to measure levels. The odd part is that you're not seeing this after being told correctly what it is several times. You don't define it with any precision yourself, Eric. -- Randy Yates % "Rollin' and riding and slippin' and Digital Signal Labs % sliding, it's magic." % http://www.digitalsignallabs.com % 'Living' Thing', *A New World Record*, ELO |
#35
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Questions on Levels
Randy Yates wrote:
(Scott Dorsey) writes: In , Randy wrote: If dBFS is defined as dBFS = 20 * log_10(XRMS / (RMS value of full-scale sine wave), where XRMS is the RMS value of the digital data stream, and you're generating a "digital square wave," then you are wrong. The digital square wave can go to +3dBFS as defined above. dBFS has not got a damn thing to do with sine waves or reference levels or anything in the analogue world. Again, I'm not asking how it's not defined, I'm asking how it is defined. You guys have danced around this one all day. It's getting humorous. It has ONLY to do with how far a digital level is below the point at which the digital value reaches full scale (all bits on). If you know what it means, and you're literate, then you should be able to come up with a precise definition. I haven't seen one yet. 0dBFs is the upper limit for an instantaneous voltage measure for the output of a system of digital to analog conversion. -- Les Cargill |
#36
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Questions on Levels
On Nov 19, 10:42*pm, (Eric Jacobsen) wrote:
On Fri, 19 Nov 2010 20:32:08 -0500, Randy Yates wrote: Mike Rivers writes: On 11/19/2010 7:52 PM, Randy Yates wrote: My question is this: What is the definition of dBFS? Decibels relative to full scale. Nonsense. All you've given is the meaning of the acronym, not an engineering definition of the unit. This is similar to stating the definition of RMS is "root mean square." [...] But it's not defined that way. I'm not asking how it's not defined. I'm asking how it is defined (in a sensible way). I think you're asking what color the sky is, and people are telling you "blue", but you're expecting a wavelength or something, so you're not accepting the answer. As you know, dB measurements are always relative to some reference level. * With dBFS the reference level is Full Scale of the converter or number system or whatever. * The ratio of the level measured to the Full Scale level provides the argument for the logarithm, and the scaled result is dBFS. If you can do dBm, or dBW, or dBC, you should be able to do dBFS. The odd part is that you're not seeing this after being told correctly what it is several times. I think you are using an inappropriate metaphor. It is more like Randy is asking what is the elephant like and the blind men are all telling him something different in these two threads. One person says 0 dBFS is a sample of all 1's and all 0's is -96 dBFS (I won't even go into what is wrong with that one)! Another describes how a VU meter works. Yet another tells him 0 dBFS is the peak clipping point (that one alone actually says somethng). None of the blind men are really right and none are wrong. In the meantime no coherent picture of the dBFS elephant has emerged and more disjointed statements are made on the topic. Another metaphor is that this is a can of worms! Rick |
#37
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Questions on Levels
On Nov 19, 7:18*pm, "Bill Graham" wrote:
"Randy Yates" wrote in message ... Hi Paul, Thank you for your answers. Comments below. PStamler writes: On Nov 18, 8:39 pm, Randy Yates wrote: 1. If you backtrack to 0 dB from this wikipedia article http://en.wikipedia.org/wiki/Line_level the reference levels for dBu and dBV are 0.775 VRMS and 1 VRMS, respectively. Is this correct? Are the reference levels I've given here exact? No and yes, respectively. The reference level for dBu is actually 0.77459666924148337703585307995648V, according to my calculator -- Wow! You have a calculator that goes to 32 significant digits? My old HP15C is only good for about 15. You can calculate the distance to Alpha Centauri to the nearest tenth of an inch...:^) It was the calculator build into WinXP. Peace, Paul |
#38
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Questions on Levels
I smell a troll.
When somebody asks a question and gets the precise answer from several people at once, and keeps on arguing that nobody has given him the answer, then a troll should be suspected. 0dBFS is the level at which one or the other extremes of a digital waveform is at maximum codeable level. There are no established standards relating that to any standards in the analog world, be they dBu, dBV, dBm or any other. There are some informal standards in the movie and broadcast world, but no standards body such as IEC or AES has adopted an official standard. And Randy, before you tell me "I don't want to know what isn't, I want to know what is," what I've written above is what is (a definition of dBFS), and there really ain't no more, and until a standards committee gets together and votes out a standard, there won't be. Peace, Paul |
#39
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Questions on Levels
In comp.dsp Eric Jacobsen wrote:
(snip, someone wrote) Nonsense. All you've given is the meaning of the acronym, not an engineering definition of the unit. This is similar to stating the definition of RMS is "root mean square." (snip) I think you're asking what color the sky is, and people are telling you "blue", but you're expecting a wavelength or something, so you're not accepting the answer. As you know, dB measurements are always relative to some reference level. With dBFS the reference level is Full Scale of the converter or number system or whatever. The ratio of the level measured to the Full Scale level provides the argument for the logarithm, and the scaled result is dBFS. But there is more to it than just the reference. Well, if you just measure one sample then that is all, but for a signal of some duration, it is more complicated. I can, for example, compute RMS for a whole CD track. I could also compute the mean of the absolute value, the geometric mean of the absolute value, or many other mathematical functions of the samples. If I have a sine that reaches peak at exactly a sample point, and reaches full scale at that point, then RMS is 5 log(2), or about 1.5dB lower. For mean absolute value, 10 log(2/pi), or about 1.96dB lower. If you can do dBm, or dBW, or dBC, you should be able to do dBFS. The odd part is that you're not seeing this after being told correctly what it is several times. -- glen |
#40
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Questions on Levels
"rickman" wrote in message ... None of the blind men are really right and none are wrong. In the meantime no coherent picture of the dBFS elephant has emerged and more disjointed statements are made on the topic. It seems to me if you realise the Bell or dB is a RELATIVE LOG term of power (and it's constituents) ratio's with no absolute UNLESS defined as a subset, (eg dBv, dBu, dBm etc) then asking for a SINGLE absolute point of reference, or single definition, is simply asking for the impossible. dBFS is simply the *Full Scale* point of ANY system so defined. IF you want it to mean anything specific, you must define it as such. MrT. |
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