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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
Ok, so I understand that 44.1k is 44,100 samples per second and 48k is
48,000 samples per second. Obviously 48,000 is better. I'm not exactly sure what bit rate is though? CDs are 16 bit, DVDs are 24. What exactly does that mean though? Another question - if I'm recording a project to audio CD, is it better to just record at 16/44 since that's what the CD will be anyway, and I can save system resources? or should I do 24/48 and then dither it down, essentially changing what I originally heard? I read in the ProTools book by Berklee Press that its best to record on LE using 24/44 since you won't hear much difference between the 48k and 44.1k. Any insights into this? --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.541 / Virus Database: 335 - Release Date: 11/14/2003 |
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
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#3
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
"Ric Oliva" wrote in message
... Ok, so I understand that 44.1k is 44,100 samples per second and 48k is 48,000 samples per second. Obviously 48,000 is better. I'm not exactly sure what bit rate is though? CDs are 16 bit, DVDs are 24. What exactly does that mean though? The term bit "rate" does contribute to the confusion. I think bit "depth" would be better. The quick answer is sampling rate (rate makes sense here) is directly related to frequency response. Bit depth is directly related to dynamic range. According to the theory, your sampling rate needs to be twice the highest frequency you want to record. So theoretically, 44.1 gives you 22kHz response, which is beyond human hearing. In practice, the actual top end limit will be somewhat lower due to analog filtering required to keep the clock noise out of the audio. But still, anything over 44.1 is probably superfluous rather than "better." Each sample has to reflect the amplitude of the signal at that sample. That value is stored in a digital "word." We're talking about storing the value in either a 16-bit or 24-bit word. The more bits, the better the resolution, which in audio is refered to as "dynamic range." Another question - if I'm recording a project to audio CD, is it better to just record at 16/44 since that's what the CD will be anyway, and I can save system resources? or should I do 24/48 and then dither it down, essentially changing what I originally heard? I read in the ProTools book by Berklee Press that its best to record on LE using 24/44 since you won't hear much difference between the 48k and 44.1k. Any insights into this? 24/44. While your finished product can sound just fine to the vast majority of ears at 16-bit depth, 24 is still worthwhile for recording, applying effects (transforms) and mastering. The reason is that the greater dynamic range of the 24-bit depth manifests itself in a lower "noise floor." This extra "room" at the bottom of your dynamic range is valuable because each time you perform any kind of transform to your audio signal(s), you'll add a bit of noise due to rounding errors. A greater bit depth makes these errors smaller, and when you resample or dither your final, mastered recording to 16-bit, most of those rounding errors will hopefully live in those truncated bits. That's not to imply that you can't do a fair number of transforms on a 16-bit file without seriously degrading it. But there is at least a good argument for using greater bit depths for recording/editing. Moreso than for higher sampling rates, anyway. -------------------------------------------------- Denny Fohringer Itinerant guitarist -------------------------------------------------- Lessons and music: http://surf.to/dennyf Bands: http://bluepearlband.com http://doubletakeband.com -------------------------------------------------- |
#4
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
What he said.
;-) "Denny F" wrote in message ... "Ric Oliva" wrote in message ... Ok, so I understand that 44.1k is 44,100 samples per second and 48k is 48,000 samples per second. Obviously 48,000 is better. I'm not exactly sure what bit rate is though? CDs are 16 bit, DVDs are 24. What exactly does that mean though? The term bit "rate" does contribute to the confusion. I think bit "depth" would be better. The quick answer is sampling rate (rate makes sense here) is directly related to frequency response. Bit depth is directly related to dynamic range. According to the theory, your sampling rate needs to be twice the highest frequency you want to record. So theoretically, 44.1 gives you 22kHz response, which is beyond human hearing. In practice, the actual top end limit will be somewhat lower due to analog filtering required to keep the clock noise out of the audio. But still, anything over 44.1 is probably superfluous rather than "better." Each sample has to reflect the amplitude of the signal at that sample. That value is stored in a digital "word." We're talking about storing the value in either a 16-bit or 24-bit word. The more bits, the better the resolution, which in audio is refered to as "dynamic range." Another question - if I'm recording a project to audio CD, is it better to just record at 16/44 since that's what the CD will be anyway, and I can save system resources? or should I do 24/48 and then dither it down, essentially changing what I originally heard? I read in the ProTools book by Berklee Press that its best to record on LE using 24/44 since you won't hear much difference between the 48k and 44.1k. Any insights into this? 24/44. While your finished product can sound just fine to the vast majority of ears at 16-bit depth, 24 is still worthwhile for recording, applying effects (transforms) and mastering. The reason is that the greater dynamic range of the 24-bit depth manifests itself in a lower "noise floor." This extra "room" at the bottom of your dynamic range is valuable because each time you perform any kind of transform to your audio signal(s), you'll add a bit of noise due to rounding errors. A greater bit depth makes these errors smaller, and when you resample or dither your final, mastered recording to 16-bit, most of those rounding errors will hopefully live in those truncated bits. That's not to imply that you can't do a fair number of transforms on a 16-bit file without seriously degrading it. But there is at least a good argument for using greater bit depths for recording/editing. Moreso than for higher sampling rates, anyway. -------------------------------------------------- Denny Fohringer Itinerant guitarist -------------------------------------------------- Lessons and music: http://surf.to/dennyf Bands: http://bluepearlband.com http://doubletakeband.com -------------------------------------------------- |
#5
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
"Ric Oliva" wrote in message
Ok, so I understand that 44.1k is 44,100 samples per second and 48k is 48,000 samples per second. Obviously 48,000 is better. Why is this obvious? I'm not exactly sure what bit rate is though? CDs are 16 bit, DVDs are 24. What exactly does that mean though? That's not bit rate. It's sample size. Another question - if I'm recording a project to audio CD, is it better to just record at 16/44 since that's what the CD will be anyway, and I can save system resources? If you are going to do very much processing, it is wise to record with 24 bit samples to preserve dynamic range as you process the tracks. After you've mixed the channels you are going to distribute, dither them down to 16 bits. or should I do 24/48 and then dither it down, essentially changing what I originally heard? Dithering down is a fast operation with most software. A proper job of downsampling can involve quite a bit of processing time. If you're going to throw away all audio 22.05 KHz in the end, why bother ever recording it? I read in the ProTools book by Berklee Press that its best to record on LE using 24/44 since you won't hear much difference between the 48k and 44.1k. Any insights into this? Yes, I just made a post entitled "Why 24/96 sampling isn't necessarily better-sounding than 24/44 sampling" that addresses this question. You can also investigate this issue yourself by downloading and listening to files of the same musical sounds recorded in various sample formats, from http://www.pcabx.com/technical/sample_rates/index.htm . |
#6
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
If sample rate is viewed as resolution over time (horizontal axis),
bit rate is resolution of the amplitude (vertical axis). Each bit doubles the resolution, or in other words, the smallest increment of volume possible is hlaved with each additional bit. The difference between 16 bits and 24 bits is 2 to eighth power, or 256. That means between each volume increment in a 16 bit recording there are 256 intermediate steps added in a 24 bit recording. This means that volume changes can be portrayed far more accurately and smoothly. Also, when you manuipulate tracks with faders and plug-ins, you are essentially doing mathematical operations, so with much higher resolution the rounding errors are minimized. In practice, the result is increased dynamic range, better stereo imaging, smoother less grainy fades and reverb tails, and less worry about having to track "hot". There is no reason not to track atr 24 bits if you can. The only disadvantage is each sound file will be 150% bigger. The difference between recording at 44.1 and 48k, on the other hand, is pretty tiny. Many people (myself included) record at 44.1 so that you don't have to worry about doing a sample rate conversion somewhere down the line (to a 44.1 CD) which may do more harm than whatever tiny gain you are getting from the slightly higher sample rate. If you are concerned with using a higher sample rate, 88.2 seems to make more sense. If you are going to do all your mixing on an analog board, however, then you might as well use 48k. |
#7
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
"Ric Oliva" wrote in message m...
Ok, so I understand that 44.1k is 44,100 samples per second and 48k is 48,000 samples per second. Obviously 48,000 is better. I'm not exactly sure what bit rate is though? CDs are 16 bit, DVDs are 24. What exactly does that mean though? Another question - if I'm recording a project to audio CD, is it better to just record at 16/44 since that's what the CD will be anyway, and I can save system resources? or should I do 24/48 and then dither it down, essentially changing what I originally heard? I read in the ProTools book by Berklee Press that its best to record on LE using 24/44 since you won't hear much difference between the 48k and 44.1k. Any insights into this? --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.541 / Virus Database: 335 - Release Date: 11/14/2003 Basically speaking, the bit resolution determines the ability to describe the amplitude of a signal. Having 24 bits available gives you a safety cushion in digital recording, among other things. The same input signal that you are slamming to 0 dbfs in 16 bit format (not a good thing because of the possibility of "overs") can be recorded in 24 bit format with the same or better resolution while staying well below the red. In a MIX article years ago, Stephen St. Croix stated that, sound improvement-wise, he'd rather have 17 bits vs. 16 instead of 96 kHz sampling rate vs. 48 kHz, if he had to make a choice. Most pro's would rather work in the higher resolutions until the absolute last bounce or mix to 16/44.1. This is partly because, with digital processing (EQ, compression, etc.), the extra headroom yields real sonic benefits when recording, editing, etc. There are some that prefer to keep everything in 44.1 all the way through to avoid sample rate conversion at the end, but there is almost universal use of higher bit resolutions whenever possible. RP |
#8
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
In article , "Ric Oliva"
wrote: Ok, so I understand that 44.1k is 44,100 samples per second and 48k is 48,000 samples per second. Obviously 48,000 is better. I'm not exactly sure what bit rate is though? CDs are 16 bit, DVDs are 24. What exactly does that mean though? http://www.promastering.com/pages/techtalk.html Article 1 and 2 deal with bit depth and dither, article 3 with sampling rates. Recording at wordlegths higher than 16 bit is helpful. In practice, 20 is almost always as good as 24 for recording since A to D converters don't have the dynamic range to capture 24 bits and the lower bits just contain the self noise of the box. For digital processing, however, you want to use longer wordlengths like 48 bit, or at the very least, 32 bit floating point. Most simply stated, wordlength (or bit depth) is dynamic range. Bit rate actually means something a little different, but we won't get into that right now as you obviously are asking about bit depth. For every bit you get about 6 dB (just over actually) of dynamic range. 16 bit CD has 96dB while 24 bit has 144. Extra bits do not add headroom; they add footroom. 0 dB FS (full scale) represents the same value in both 16 bit and 24 bit audio. The extra bits come into play at the bottom of the range. You are able to record smaller events - sounds at a lower level. In addition to dynamic range, it also means noise. in 16 bit, there is a noise floor of -96dB while 24 bit has a noise floor of -144 dB. 24 bit offers no additional accuracy in the top 96db of the dynamic range. Actually, an 8 bit recording is just as accurate as a 24 bit recording from 0dBFS to -48 dB. The -48 dB noise floor is quite obtrusive and the 8 bit recording certainly sounds worse, but those top 48 dB are just as accurate as a 24 bit recording. If you took a 24 bit file and added 96 dB of noise, it would sound like an 8 bit file. Invariably any discussion of bit depths must eventually include dither. This, however, I'll leave to the tech talk articles I've pointed you to, or to a google search for the many posts that have appeared here in r.a.p. Be aware, however, that there are some common mistakes made quite often when discussing these subjects, so avoid the myths. Sometimes common sense tends to fail you until you understand how digital audio truly works, so some things that seem to make intuitive sense at first are actually technical rubbish. -- Jay Frigoletto Mastersuite Los Angeles promastering.com |
#9
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
Jay - atldigi wrote:
In article , "Ric Oliva" wrote: Ok, so I understand that 44.1k is 44,100 samples per second and 48k is 48,000 samples per second. Obviously 48,000 is better. I'm not exactly sure what bit rate is though? CDs are 16 bit, DVDs are 24. What exactly does that mean though? http://www.promastering.com/pages/techtalk.html Article 1 and 2 deal with bit depth and dither, article 3 with sampling rates. Recording at wordlegths higher than 16 bit is helpful. In practice, 20 is almost always as good as 24 for recording since A to D converters don't have the dynamic range to capture 24 bits and the lower bits just contain the self noise of the box. For digital processing, however, you want to use longer wordlengths like 48 bit, or at the very least, 32 bit floating point. Most simply stated, wordlength (or bit depth) is dynamic range. Bit rate actually means something a little different, but we won't get into that right now as you obviously are asking about bit depth. For every bit you get about 6 dB (just over actually) of dynamic range. 16 bit CD has 96dB while 24 bit has 144. Extra bits do not add headroom; they add footroom. 0 dB FS (full scale) represents the same value in both 16 bit and 24 bit audio. The extra bits come into play at the bottom of the range. You are able to record smaller events - sounds at a lower level. In addition to dynamic range, it also means noise. in 16 bit, there is a noise floor of -96dB while 24 bit has a noise floor of -144 dB. 24 bit offers no additional accuracy in the top 96db of the dynamic range. Actually, an 8 bit recording is just as accurate as a 24 bit recording from 0dBFS to -48 dB. The -48 dB noise floor is quite obtrusive and the 8 bit recording certainly sounds worse, but those top 48 dB are just as accurate as a 24 bit recording. If you took a 24 bit file and added 96 dB of noise, it would sound like an 8 bit file. Invariably any discussion of bit depths must eventually include dither. This, however, I'll leave to the tech talk articles I've pointed you to, or to a google search for the many posts that have appeared here in r.a.p. Be aware, however, that there are some common mistakes made quite often when discussing these subjects, so avoid the myths. Sometimes common sense tends to fail you until you understand how digital audio truly works, so some things that seem to make intuitive sense at first are actually technical rubbish. So, what answer is correct? Whiteswan, Rick Powell, and Jay have given three answers that sound good but are mutually exclusive. I've been at this a few years and I still don't know what is right. Does 24 bit give greater resolution than 16 bit or does it merely give a larger dynamic range without a finer resolution? Peter |
#10
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
Peter Gemmell wrote: So, what answer is correct? Whiteswan, Rick Powell, and Jay have given three answers that sound good but are mutually exclusive. I've been at this a few years and I still don't know what is right. Does 24 bit give greater resolution than 16 bit or does it merely give a larger dynamic range without a finer resolution? The way that finer resolution manifests is as a larger signal to noise ratio. The noise is due to quantization and the wider the sample, the lower the noise is relative to the maximum representable signal. The noise is an approximately random error of +-1/2 the value of the low order bit. It is inescapable. It is intimately related to the dynamic range because it determines how small the signal can be before it loses signifigance relative to that error noise limit. The ratio of how large a signal that can be represented to how small a signal can be represented is the dynamic range. In practice, I don't think that yet any front end to a 24 bit ADC is itself nearly as quiet as that quantization noise so that you will see specifications, if they are honest, that are signifigantly lower than the theoretical 144 dB SNR that can be achieved with 24 bits. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#11
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
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#12
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
"Jay - atldigi" wrote in message
White Sawn's satement seems to indicate that the extra bits are within the same dynamic range, thereby giving you greater detail within that range. You can't into the trap of viewing digital audio like it's digital imagery. Unfortunately, 24 bits leaves the top 96db range of 16 bit alone, but lowers the noise floor and allows the recording of audio events that are even smaller, at a lower level, i.e. below -96dB. 24 bits puts 16 extra levels between each pair of levels that exist with 16 bits. Thus, the resolution is increased at any level, not just the smallest one. The reduction of the noise floor due to 24 bits is a consequence of the extra resolution 24 bit coding provides between any of the two levels in a 16 bit representation. The two go together hand-in-hand because the coding is linear. The idea that adding bits does not increase resolution is yet another popular urban myth about digital. It's similar to the urban myth that analog has resolution below the noise floor. In an exactly linear system, whether digital or analog, the noise floor and resolution are exactly the same. In a nominally linear (i.e., real-world) system, whether digital or analog, the noise floor and resolution are nominally the same. |
#13
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
Jay - atldigi wrote in message ...
Rick understands that bit depth relates to amplitude and that DSP is better with longer wordlengths. A small clarification is in order, however. He seems to consider there to be extra headroom while technically there is not, unless you change the zero reference. In other words, increase the voltage that zero is referenced to. Nevermind working at -10 or +4, you'll be using a new, nonstandard reference voltage, and what about the analog electronics that probably can't handle that voltage? You're asking for trouble for that reason and several others (increasing the noise floor of the analog gear, compatability, and more). Unless you want to do that, you really are gaining what should be thought of as "footroom" more than headroom. In practice some feel that you need to push a digital recording right up to 0dB FS to "use all the bits". This really isn't as big an issue as some would have you believe, as long as you use good gain stageing and reasonable recording levels, especially with todays converters which perform far better than much or the early crappy digital stuff. It doesn't hurt to assumne that 24 bits gives you a little room to play with, but unless you are recording a program with greater than average dynamic range in a very quiet environment with excellent equipment and minimal processing, you really aren't going to be able to take advantage of those extra bits. Then again, they certainly don't hurt, and they could help, so there's no reason not to. Still, it helps to understand technically what's going on and when extra effort will pay off and when if won't. Jay, I'm not suggesting changing the zero reference. Correct the following if I'm wrong, but as a mastering engineer, you would rather take in a 2-track digital mix that peaked at -2db than one that peaks at 0 dbfs and has a few "flat tops". Using a 24 bit format to record or mix down to allows less artifacts towards the noise floor, given 2 "identical" sources (one recorded at 16 bit and one at 24 bit) peaking at, say, -2db. And reduces the need (perceived or real) to "slam" the recording all the way to 0 dbfs to take "full advantage" of the bit depth. If this is "footroom' instead of "headroom", isn't it still a margin nonetheless? RP |
#14
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
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#16
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
Ric Oliva wrote:
Ok, so I understand that 44.1k is 44,100 samples per second and 48k is 48,000 samples per second. Obviously 48,000 is better. I'm not exactly sure what bit rate is though? CDs are 16 bit, DVDs are 24. What exactly does that mean though? Another question - if I'm recording a project to audio CD, is it better to just record at 16/44 since that's what the CD will be anyway, and I can save system resources? or should I do 24/48 and then dither it down, essentially changing what I originally heard? I read in the ProTools book by Berklee Press that its best to record on LE using 24/44 since you won't hear much difference between the 48k and 44.1k. Any insights into this? The minimum necessary sample rate and bit depth is determined by the sounds you want to reproduce. The dynamic range (basically signal-to-noise ratio) of your material determines the minimum necessary bit depth. In practice, you will never record a source with a dynamic range greater than can be represented in 16 bits. The bandwidth (frequency range) determines the necessary sample rate. The sample rate is required only to be more than double the highest frequency you want to reproduce. In practice, almost nobody owns reproduction equipment that is useful beyond 20kHz. So in theory you can record at 44.1/16 and your digital audio will hold all of the audio data necessary to reproduce anything you can put into and pull out of any equipment. The need for greater data rates comes when you plan to manipulate the recording one or more times between the record and reproduce moments. If you are going to re-sample your data (through sample rate conversion or a D/A-A/D process), then you might benefit from an increased sample rate. More importantly, if you plan to manipulate the VALUES of those existing samples (by DSP processes such as gain changes, EQ, or anything else), then you might benefit from an increased bit depth. Both of these considerations serve to push the limitations of the quantization processes beyond our ability to detect them. The idea is that stacking these processes can compound their inherent errors and eventually make them audible. Even this precaution represents a judicious level of overkill in almost all cases, but data storage is getting cheap so it doesn't hurt. In summary: If you're recording live to 2-track and won't be doing any processing at all, then 44.1/16 is more than adequate. If you will be doing any processing, then start with 24 bits. If you will be doing any resampling, then start with 96k. Whatever rate you choose for your initial recording, you should maintain that rate until the final stage of processing. |
#17
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
"Ric Oliva" wrote in message ... Ok, so I understand that 44.1k is 44,100 samples per second and 48k is 48,000 samples per second. Obviously 48,000 is better. Correct. The more samples of a waveform you can gather, the easier it is to reproduce it. I'm not exactly sure what bit rate is though? CDs are 16 bit, DVDs are 24. What exactly does that mean though? That's not bit rate, but rather bit depth. MP3 files and other audio file formats are often saved in a format determined by "bit rate", so as to determine the number of bits per actual chunk of time--hence, an HTTP download of an MP3 file can be streamed with highest quality possible if the bit rate is predetermined. Bit depth, however, is the vertical sampling resolution of an audio sample. As you know, 44kHz sample rate is the number of samples per second. On a horizontal waveform drawing, this is the horizontal resolution (think screen resolution on your monitor, 640x480 vs. 1024x768). Bit depth is the number of bits of information per sample, or the vertical resolution. For example, in an 8-bit sample bit depth, a waveform's amplitude in a particular sample can be in any of 256 possible positions (2*8 = 256). Obviously, that's a very small number of possibilities. So a 16-bit sample bit depth the resolution is much higher: 65536. Bit rate is determined by the two resolutions combined. Theoretically, an MP3 file saved with a 64kbps bit rate means that the file must be downloaded from the Internet at a rate of at least 64 kilobits per second in order for it to be streamed through the MP3 player without hiccupping. Another question - if I'm recording a project to audio CD, is it better to just record at 16/44 since that's what the CD will be anyway, and I can save system resources? or should I do 24/48 and then dither it down, essentially changing what I originally heard? In general, with audio it is better to sample at high depth and resolution and then downgrade afterwards than it is to stay true to the final output. Jon |
#18
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
In general, with audio it is better to sample at high depth and resolution
and then downgrade afterwards than it is to stay true to the final output. Jon I followed all the postings, and there are a lot of fine comments out there. I guess I'll add my 2 bits: First, going back to some of the earlier dither comments: The concept of digital dither was covered pretty well - word length reduction. I would probably magnify the fact that reduction with no dither causes 2 bad things. The first is harmonic distortions, the second is noise modulation. Think for a second of a tiny sine wave, less than 1 quantization peak to peak, residing between 2 quantization levels. It yields nothing. That is and incorect result. Now shift it so it "seats" on a quantization level, going over and under and over and under... by only one bit. That gives you a 1 bit amolitude square wave... This is not a good signal either... This is just a starting point to think about. Again you can see pictures on www.lavryengineering.com (under suport, "Do you need 20 Bits" artical. But I was more interested in analog dither. Years ago, I was experimenting with in. Some of it was around Nyquist frequencies, some was "subtuctive dither" (remove much in the digital domain what you injected in the analog domain). Why analog dither? Well, nothing happens if you feed a signal into a circuit and it does not cvause some digital transitions... Say your circuit generates a different code every 1 millivolt, but the signal is small and is always between 5.1 and 5.7mV... No action. So you need to "force it" to go over and under some threshold (transition) levels. So we add noise. It does get pretty complicated in a hurry. First knee jerk reaction is to add all the noise in high frequncey. It is not that simple, because after truncation, a lot of the high frequncey reapears in the audio range. But you "have to do somthing"- add some random noise, thus trade off some noise (dynamic range). For word reduction it is done to fix the distortions and noise modulation problems. On the analog side, it was about "getting anything to move" (and more than that). So the question beacme, was is the best tradeoff? Least energy added for fixing the problem? That was when triangle dither (2 least significant bits peak to peak) solution came about. But than there was a period where analog dither died (at least for me). The quantization levels got so close to each other, that the circuit noise was way bigger than I wished for. Take say a 10V range and try for 20 bits - 10uV steps (10 microvolts). Getting the signal in there with such low noie (10 uV peak to peak) is not a walk in the park... You "call" the noise "too much dither" and move farward... But than analog dither came back - BIG TIMES! It started with 1 bit (like DSD) and is now an everyday thing wth the newer multibit ADC's. Those have just very few bits, thus the quantization levels are very far apart. No longer in the microvolts, but in the volts (or near it). This are all noise shaping converters. You feed back a filtered quantized output and subtuct from the input.. This will take too long to explain, but such a raw structure will have all sorts of problems thus it requires dither, and often very large amplitude. The dither randomness tend to "break up" what would otherwise be consistant repetative patterns (called limit cycles), not exactly what you want in the audio... Regarding the comments on dynamic range and bits. Yes it was well said, and about 6dB per bit is right. So 24 bits is about 144dB, and we can all realize it is also a bit of crock. My AD122 MKII has the largest dynamic range (127dB unweighted) so it is 21+ bits. My first generation AD122 had 122dB (20 bits) and I called it a 20 bit converter. Than all those 100-110dB devices apeared on the market with "24 bits" on the panel and the sales guys insisted that I call mine a 24 bits. The bits are there, but the last few just bounce around mindlesly - no realtion to the audio. I have a cheap circuit for andom number generation. If I add 100 bits of noie at the thend (least significant bits) will it be a 124 bits machine? Lets go for it I could probably design a 24 bit AD, and it will be an unbelivable energy hog. Remember that we are on a log scale. The differance between 20 and 24 is not "just 4 more". It is a factor of 16 more. Sort of like a 6 earthquake vs an 8 earthquake. Big differance. Do you need 24 bits AD? Probably not, short of some of the headroom comments. What is the best Mic preamp out there? Say -130dBu? How much gain is it set for? Say I use 30dB gain, than the noise floor is at -100dBu and a peak to peak siganl out of the preampp is 24Bu driving an AD. So we have 100+24=124dB dynamic range. My AD122 MKII gives you 3dB margin. But say you need 40dB mic pre gain. Now you can use the 114dB dynamic range device... I am not a recording engineer, but I think that 127dB is already only for close mics that put out serious signal followed by a great mic pre... While I rather have folks specify dynamic range (not bits), the 24 bit number is pretty good in the sense that it is a multiple of 8 bits (thus 3 bytes). It is a good number for computers and hardware (multiple of 8). I just wish 24 bits did not get used by industry salesman as measure of quality. Last comment for now: Whatever I said regarding 24 bits and what is needed is ONLY for AD's and DA's. Let me call them CONVERSION BITS. There are other type of bits. Let me call them PROCESSING BITS. If 24 conversion bits may be an overkill, 24 processing bits is way too little. Folks need to realize it. A guy comes with some digital EQ and tells you that it has 56 bits, or 32 floating point DSP, and he does have a point to make. Just do not later go and look for a 56 bits AD... Different issue. I think it was already explained, but here we go: Say I want to avarage 50 cent (money) and 51 cent. It is 50.5 cents. I can only deal with cents so we either call it 50 or 51. We have 1/2 cent inacuracy. In a bianry wold, I lost a bit of acuracy. So lets agree to have a new coin - 1/2 cent. Now we avarage 50, 50 and 51. It yields 50.3333333... Well ae can call it 50 or 50.5.... The general statment is that when you add more and more computations, you reduce more and more of the accuracy. So yes, we typicaly need a lot of computational bits. To all, pardon me if soem of the above is a repeat of what you said, I tried to fill some gaps, and probably covered things that needed no help. I am new to audio NG. BR Dan Lavry |
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
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#21
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16 bit vs 24 bit, 44.1khz vs 48 khz <-- please explain
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