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#1
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Nyquist filters at different sample rates.
One of the advantages of recording at 96000Hz, is that
there is more room between the highest needed captured frequency, and the Nyquist frequency, and so does not need to have so steep a curve, which is of some benefit of a nature that escapes me at the moment. Do most devices actually change filters then, based on current sample rate, or do they just have one that works with 44100, and call that good for everything? Thanks, Tobiah |
#2
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Nyquist filters at different sample rates.
and so does not need to have so steep a curve, I meant the curve of the low-pass filter that is used to avoid crossing the Nyquist on the way into the ADC. |
#3
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Nyquist filters at different sample rates.
On Mon, 15 Aug 2011 08:52:26 -0700, Tobiah
wrote: One of the advantages of recording at 96000Hz, is that there is more room between the highest needed captured frequency, and the Nyquist frequency, and so does not need to have so steep a curve, which is of some benefit of a nature that escapes me at the moment. Do most devices actually change filters then, based on current sample rate, or do they just have one that works with 44100, and call that good for everything? Thanks, Tobiah I have an Arcam CD player that changes the nature of the filter dynamically in response to the programme material. It is so good that I have never heard a difference between it and a normal CD player. Recovering audio from digital sources is by now such a done deal that you really need not worry about exotic sampling rates etc. d |
#4
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Nyquist filters at different sample rates.
"Tobiah" wrote in message ... One of the advantages of recording at 96000Hz, is that there is more room between the highest needed captured frequency, and the Nyquist frequency, and so does not need to have so steep a curve, which is of some benefit of a nature that escapes me at the moment. Do most devices actually change filters then, based on current sample rate, or do they just have one that works with 44100, and call that good for everything? Most modern DACs implement the brick wall low pass filter that provides a sharp cutoff just below the Nyquist frequency with a digital filter that naturally changes its corner frequency to suit the sampling frequency. |
#5
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Nyquist filters at different sample rates.
Tobiah wrote:
One of the advantages of recording at 96000Hz, is that there is more room between the highest needed captured frequency, and the Nyquist frequency, and so does not need to have so steep a curve, which is of some benefit of a nature that escapes me at the moment. Well, that was true in the 1980s, but today we use oversampling and we don't have to worry about that junk. Do most devices actually change filters then, based on current sample rate, or do they just have one that works with 44100, and call that good for everything? If they are properly made. Some (Panasonic) equipment traditionally did not change the filters properly and so sounded dramatically different at different sample rates. But today we use oversampling and we don't worry about it. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#6
Posted to rec.audio.pro
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Nyquist filters at different sample rates.
One of the advantages of recording at 96000Hz, is that
there is more room between the highest needed captured frequency, and the Nyquist frequency, and so does not need to have so steep a curve, which is of some benefit of a nature that escapes me at the moment. CDs are cut at 44.1kHz, so 88.2kHz and 176.4kHz are preferable to 96kHz and 192kHz, as no compensation for a non-integral change in sample rate is needed (eg, interpolation, etc). Of course, BD and more-recent formats natively support 96kHz and 192kHz, so, recordings made for them would naturally use the higher rates. |
#7
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Nyquist filters at different sample rates.
On 8/20/2011 5:07 PM, William Sommerwerck wrote:
CDs are cut at 44.1kHz, That much is correct. so 88.2kHz and 176.4kHz are preferable to 96kHz and 192kHz, as no compensation for a non-integral change in sample rate is needed (eg, interpolation, etc). That's not correct, unless you want to do a half-assed job of sample rate conversion. You always need to re-sample, you can't just leave out every other sample and end up with the same waveform less any content above the Nyquest frequency limit. Don't press me for a citation, I just know these things because I'm smart. I'm surprised that you don't know this, because you're pretty smart yourself. -- "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 |
#8
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Nyquist filters at different sample rates.
"Mike Rivers" wrote in message
... On 8/20/2011 5:07 PM, William Sommerwerck wrote: CDs are cut at 44.1kHz, That much is correct. so 88.2kHz and 176.4kHz are preferable to 96kHz and 192kHz, as no compensation for a non-integral change in sample rate is needed (eg, interpolation, etc). That's not correct, unless you want to do a half-assed job of sample rate conversion. You always need to re-sample, you can't just leave out every other sample and end up with the same waveform less any content above the Nyquest frequency limit. Don't press me for a citation, I just know these things because I'm smart. I'm surprised that you don't know this, because you're pretty smart yourself. If one is down-converting to a rate that's an integral fraction (yes, that sounds dumb), there's no need to create "in-between" samples. But when you go from (say) 96kHz to 44.1kHz, you have generate and interpolate appropriate samples. Regardless of the sample rate, the original digital data have to be filtered for the Nyquist frequency of the lower rate before resampling. |
#9
Posted to rec.audio.pro
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Nyquist filters at different sample rates.
"William Sommerwerck" wrote in message
... "Mike Rivers" wrote in message ... On 8/20/2011 5:07 PM, William Sommerwerck wrote: CDs are cut at 44.1kHz, That much is correct. so 88.2kHz and 176.4kHz are preferable to 96kHz and 192kHz, as no compensation for a non-integral change in sample rate is needed (eg, interpolation, etc). That's not correct, unless you want to do a half-assed job of sample rate conversion. You always need to re-sample, you can't just leave out every other sample and end up with the same waveform less any content above the Nyquest frequency limit. Don't press me for a citation, I just know these things because I'm smart. I'm surprised that you don't know this, because you're pretty smart yourself. If one is down-converting to a rate that's an integral fraction (yes, that sounds dumb), there's no need to create "in-between" samples. But when you go from (say) 96kHz to 44.1kHz, you have generate and interpolate appropriate samples. Or more precisely, the minimum interpolation rate is the same as the starting rate when it's a 2:1 downsample. There's no need to interpolate up by a factor of 2 so you can decimate by a factor of 4. Regardless of the sample rate, the original digital data have to be filtered for the Nyquist frequency of the lower rate before resampling. For quick and dirty work (like telephony codecs) simply averaging the samples removes some of the artifacts for 2:1 resample, which is usually good enough for those applications. But agreed, you always need a digital low pass filter to remove all of the artifacts. Sean |
#10
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Nyquist filters at different sample rates.
If one is down-converting to a rate that's an integral fraction (yes,
that sounds dumb), there's no need to create "in-between" samples. But when you go from (say) 96kHz to 44.1kHz, you have generate and interpolate appropriate samples. Or more precisely, the minimum interpolation rate is the same as the starting rate when it's a 2:1 downsample. There's no need to interpolate up by a factor of 2 so you can decimate by a factor of 4. I'm not sure the point is coming across. Data at 96k samples/second cannot be /directly/ downconverted to 44.1k, because the higher rate is not an intergral multiple of the lower. The smaples only line up every (LCM of 96 and 44.1) samples. You have to create "in-between" samples. Their values will vary, depending on whether you use linear interpolation, or something else. |
#11
Posted to rec.audio.pro
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Nyquist filters at different sample rates.
On 8/21/2011 12:10 PM, William Sommerwerck wrote:
If one is down-converting to a rate that's an integral fraction (yes, that sounds dumb), there's no need to create "in-between" samples. But when you go from (say) 96kHz to 44.1kHz, you have generate and interpolate appropriate samples. Or more precisely, the minimum interpolation rate is the same as the starting rate when it's a 2:1 downsample. There's no need to interpolate up by a factor of 2 so you can decimate by a factor of 4. I'm not sure the point is coming across. Data at 96k samples/second cannot be /directly/ downconverted to 44.1k, because the higher rate is not an intergral multiple of the lower. The smaples only line up every (LCM of 96 and 44.1) samples. You have to create "in-between" samples. Their values will vary, depending on whether you use linear interpolation, or something else. From Wiki: http://en.wikipedia.org/wiki/Sample_rate_conversion It appears the main advantage to having the two sample rates being an integer multiple of one another, is that the least common multiple is simply the larger of the two numbers (using method "a"). For 96 and 44.1, although 96/44.1 is still a rational number(960/441), the least common multiple frequency is some huge number. So in this case, it would appear the linear interpolation of method "b" would be preferred. But since in method "a", a digital FIR filter must be applied at the Nyquist of the lower frequency, I don't know if there is a significant difference in computation time between the two. |
#12
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Nyquist filters at different sample rates.
On 8/21/2011 7:14 PM, Paul wrote:
On 8/21/2011 12:10 PM, William Sommerwerck wrote: If one is down-converting to a rate that's an integral fraction (yes, that sounds dumb), there's no need to create "in-between" samples. But when you go from (say) 96kHz to 44.1kHz, you have generate and interpolate appropriate samples. Or more precisely, the minimum interpolation rate is the same as the starting rate when it's a 2:1 downsample. There's no need to interpolate up by a factor of 2 so you can decimate by a factor of 4. I'm not sure the point is coming across. Data at 96k samples/second cannot be /directly/ downconverted to 44.1k, because the higher rate is not an intergral multiple of the lower. The smaples only line up every (LCM of 96 and 44.1) samples. You have to create "in-between" samples. Their values will vary, depending on whether you use linear interpolation, or something else. From Wiki: http://en.wikipedia.org/wiki/Sample_rate_conversion It appears the main advantage to having the two sample rates being an integer multiple of one another, is that the least common multiple is simply the larger of the two numbers (using method "a"). For 96 and 44.1, although 96/44.1 is still a rational number(960/441), the least common multiple frequency is some huge number. The least common multiple frequency of 96k and 44.1k is 14.112MHz: http://www.mathsisfun.com/least-comm...iple-tool.html So you'd take the 96k signal, add 146 zeros to each bit, apply the FIR filter at the Nyquist of 44.1k (cut-off at 22.05kHz), and then take only every 320th sample. But with modern computing power, perhaps this wouldn't be that much slower than the interpolation method "b". |
#13
Posted to rec.audio.pro
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Nyquist filters at different sample rates.
William Sommerwerck wrote:
One of the advantages of recording at 96000Hz, is that there is more room between the highest needed captured frequency, and the Nyquist frequency, and so does not need to have so steep a curve, which is of some benefit of a nature that escapes me at the moment. CDs are cut at 44.1kHz, so 88.2kHz and 176.4kHz are preferable to 96kHz and 192kHz, as no compensation for a non-integral change in sample rate is needed (eg, interpolation, etc). Of course, BD and more-recent formats natively support 96kHz and 192kHz, so, recordings made for them would naturally use the higher rates. From a thread at PRW: "88.2 divides into 44.1 with a nice, simple 2 but 96 does not, so SRC for 96Khz must be more complex, right? However, that is not how SRC works. All the upper rates are upsampled even further until a number that can be commonly divided between it and the desired lower sample rate is reached. THEN the math is done and the sample is converted. So in the end, the math is simple(r) than it appears, even for apparently non divisible rates." -- shut up and play your guitar * http://hankalrich.com/ http://www.youtube.com/walkinaymusic http://www.sonicbids.com/HankandShaidri |
#14
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Nyquist filters at different sample rates.
In article , Paul wrote:
So you'd take the 96k signal, add 146 zeros to each bit, apply the FIR filter at the Nyquist of 44.1k (cut-off at 22.05kHz), and then take only every 320th sample. This is the old-style "filter and decimate" algorthm. It requires little CPU. I am using it on an 8051 taking low frequency data right now. But with modern computing power, perhaps this wouldn't be that much slower than the interpolation method "b". Not to mention that we have plenty of dedicated interpolation hardware now, so it doesn't even need to be done in software. The AD1890 has spawned many children. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#15
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Nyquist filters at different sample rates.
On 8/22/2011 11:40 AM, Scott Dorsey wrote:
In , wrote: So you'd take the 96k signal, add 146 zeros to each bit, apply the FIR filter at the Nyquist of 44.1k (cut-off at 22.05kHz), and then take only every 320th sample. This is the old-style "filter and decimate" algorthm. It requires little CPU. I am using it on an 8051 taking low frequency data right now. But with modern computing power, perhaps this wouldn't be that much slower than the interpolation method "b". Not to mention that we have plenty of dedicated interpolation hardware now, so it doesn't even need to be done in software. The AD1890 has spawned many children. --scott Sample rate conversion is still done in software for DAWs, but yeah, there are hardware things like this: http://www.cirrus.com/en/pubs/proDat.../CS8420_F4.pdf Interesting stuff.... |
#16
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Nyquist filters at different sample rates.
On Mon, 22 Aug 2011 12:28:10 -0700, Paul wrote:
On 8/22/2011 11:40 AM, Scott Dorsey wrote: In , wrote: So you'd take the 96k signal, add 146 zeros to each bit, apply the FIR filter at the Nyquist of 44.1k (cut-off at 22.05kHz), and then take only every 320th sample. This is the old-style "filter and decimate" algorthm. It requires little CPU. I am using it on an 8051 taking low frequency data right now. But with modern computing power, perhaps this wouldn't be that much slower than the interpolation method "b". Not to mention that we have plenty of dedicated interpolation hardware now, so it doesn't even need to be done in software. The AD1890 has spawned many children. --scott Sample rate conversion is still done in software for DAWs, but yeah, there are hardware things like this: http://www.cirrus.com/en/pubs/proDat.../CS8420_F4.pdf Interesting stuff.... Most hardware converters are in fact software - simply permanently blown into a micro. It is actually a pretty blurred line between hardware and software. d |
#17
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Nyquist filters at different sample rates.
On 8/22/2011 1:04 PM, Don Pearce wrote:
On Mon, 22 Aug 2011 12:28:10 -0700, wrote: On 8/22/2011 11:40 AM, Scott Dorsey wrote: In , wrote: So you'd take the 96k signal, add 146 zeros to each bit, apply the FIR filter at the Nyquist of 44.1k (cut-off at 22.05kHz), and then take only every 320th sample. This is the old-style "filter and decimate" algorthm. It requires little CPU. I am using it on an 8051 taking low frequency data right now. But with modern computing power, perhaps this wouldn't be that much slower than the interpolation method "b". Not to mention that we have plenty of dedicated interpolation hardware now, so it doesn't even need to be done in software. The AD1890 has spawned many children. --scott Sample rate conversion is still done in software for DAWs, but yeah, there are hardware things like this: http://www.cirrus.com/en/pubs/proDat.../CS8420_F4.pdf Interesting stuff.... Most hardware converters are in fact software - simply permanently blown into a micro. It is actually a pretty blurred line between hardware and software. True... |
#18
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Nyquist filters at different sample rates.
On 8/22/2011 4:04 PM, Don Pearce wrote:
Most hardware converters are in fact software - simply permanently blown into a micro. It is actually a pretty blurred line between hardware and software. That's true, but it's a black box that you can't screw up too badly and it never needs an updated driver because the operating system or the I/O ports never change. -- "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 |
#19
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Nyquist filters at different sample rates.
"Don Pearce" wrote in message
... On Mon, 22 Aug 2011 12:28:10 -0700, Paul wrote: Most hardware (sample rate) converters are in fact software - simply permanently blown into a micro. It is actually a pretty blurred line between hardware and software. The increasing power and programmability of CPUs at low prices and small sizes is only going to make that more and more true. Not too many people have thought seriously about using a general purpose CPU chip as a component of a sub $100 audio widget until lately, but the price/size/power/performance revolution fostered by ARM processors has changed all of that. |
#20
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Nyquist filters at different sample rates.
On Tue, 23 Aug 2011 08:34:23 -0400, "Arny Krueger"
wrote: "Don Pearce" wrote in message ... On Mon, 22 Aug 2011 12:28:10 -0700, Paul wrote: Most hardware (sample rate) converters are in fact software - simply permanently blown into a micro. It is actually a pretty blurred line between hardware and software. The increasing power and programmability of CPUs at low prices and small sizes is only going to make that more and more true. Not too many people have thought seriously about using a general purpose CPU chip as a component of a sub $100 audio widget until lately, but the price/size/power/performance revolution fostered by ARM processors has changed all of that. The "hard wired software" aspect is even greater now that some of these micros are no longer programmed in native machine code, but in a more or less high level language. This presupposes some built in operating system, which may well be blown into the micro along with the working code. d |
#21
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Nyquist filters at different sample rates.
On Mon, 22 Aug 2011 18:56:40 -0400, Mike Rivers
wrote: On 8/22/2011 4:04 PM, Don Pearce wrote: Most hardware converters are in fact software - simply permanently blown into a micro. It is actually a pretty blurred line between hardware and software. That's true, but it's a black box that you can't screw up too badly and it never needs an updated driver because the operating system or the I/O ports never change. Do you remember "permanently greased bearings"? They were identical to ordinary bearings, but made cheaper by not having grease nipples. This is exactly the same thing. d |
#22
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Nyquist filters at different sample rates.
On 8/23/2011 3:45 PM, Don Pearce wrote:
Do you remember "permanently greased bearings"? They were identical to ordinary bearings, but made cheaper by not having grease nipples. This is exactly the same thing. I had to replace some of those in a car that I apparently kept too long. When I commented about them being "lifetime lubricated" the mechanic said "that was for the life of the bearing, not the life of the car." -- "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
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Nyquist filters at different sample rates.
"William Sommerwerck" wrote in message
... If one is down-converting to a rate that's an integral fraction (yes, that sounds dumb), there's no need to create "in-between" samples. But when you go from (say) 96kHz to 44.1kHz, you have generate and interpolate appropriate samples. Or more precisely, the minimum interpolation rate is the same as the starting rate when it's a 2:1 downsample. There's no need to interpolate up by a factor of 2 so you can decimate by a factor of 4. I'm not sure the point is coming across. Referring to your first point above from 88.2 to 44.1. Sean |
#24
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Nyquist filters at different sample rates.
"Mike Rivers" wrote in message ... On 8/23/2011 3:45 PM, Don Pearce wrote: Do you remember "permanently greased bearings"? They were identical to ordinary bearings, but made cheaper by not having grease nipples. This is exactly the same thing. I had to replace some of those in a car that I apparently kept too long. When I commented about them being "lifetime lubricated" the mechanic said "that was for the life of the bearing, not the life of the car." When was the last time you had to replace a wheel bearing in a car, before that? I've logged well over 100,000 miles in at least a half dozen cars, close to 200,000 in several, and had to replace exactly one wheel bearing. The one bearing I replaced was arguably abused when I encountered severe wheel hop trying to climb an icy road maybe a decade before it failed. If you are old enough and were hands-on with cars enough, you can remember repacking all 4 wheel bearings. I can't remember the exact interval back in the 60s, maybe 40,000 miles. At one time the interval was 1,000 miles, if memory serves related to studying really old car maintenance manuals. |
#25
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Nyquist filters at different sample rates.
On 8/24/2011 6:24 AM, Arny Krueger wrote:
When was the last time you had to replace a wheel bearing in a car, before that? I don't even think of wheel bearings any more, but I remember repacking them by hand. I did have a "permanent" rear wheel bearing go out on a car that had less than 100,000 miles on it. It was covered under the warranty. I was thinking about the suspension and steering links that used to get greased every time you changed the oil. I haven't lubricated one of those, and had only one that was worn enough to worry about (but I got rid of the car before fixing it) in the last 20 years. I think the last car I had that had grease fittings was my 1972 240Z. It came with plug, and at 20,000 miles or so, you were supposed to take them out, put in grease fittings, and lubricate it. Then you were supposed to remove the fittings and put the plugs back in, but I just left it so it could be maintained. Kind of like when replacing an IC, installing a socket. -- "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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