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Are high sample rates better for DSP?
Ethan Winer
post Jun 10 2012, 20:13
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I've read many times that audio plug-ins such as equalizers work better at higher sample rates, even if audio generally doesn't benefit. It seems unlikely that there's a practical advantage to up-sampling all your files, or recording at 96 KHz in the first place, but is there a potential theoretical improvement? Or is this just another Internet myth?

--Ethan


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benski
post Jun 10 2012, 21:17
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Yes, many filters work better with higher sampling rates. Particularly resonant filters (of the kind used in EQ) as well as filters feedback paths, such as emulations of analog filters. Many of these kinds of filters are only accurate (desired Fc versus actual Fc) and stable up to perhaps 1/8 Fs. With certain filter topologies, the filter cutoff point and resonance self-oscillation frequency start to drift apart at higher frequencies, also.

For these reasons, it is much better to oversample the input before the filters so that the audio band lies within the "good" range of the filter.

Unfortunately, good resampling is often slow, and more importantly, latent, so it can at times be more advantageous to simply run the whole processing chain at some high sampling frequency, e.g. 384kHz.


Also: non-linear effects, such as distortion, will almost always alias. Certain effects that seem linear are actually not, as fast modulation of parameters such as gain (for a compressor/expander) or filter cutoff (wah pedal) will introduce aliasing as well. Oversampling reduces aliasing in the audio band, as the aliased signal typical falls off 6dB/octave.

This post has been edited by benski: Jun 10 2012, 21:21
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Ethan Winer
post Jun 11 2012, 17:18
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QUOTE (knutinh @ Jun 10 2012, 15:46) *
The higher the sample-rate, the better any approximations that assume that the sample-rate is infinite (or that logic propagation speed is infinite) will be.


QUOTE (benski @ Jun 10 2012, 16:17) *
non-linear effects, such as distortion, will almost always alias. Certain effects that seem linear are actually not, as fast modulation of parameters such as gain (for a compressor/expander) or filter cutoff (wah pedal) will introduce aliasing as well. Oversampling reduces aliasing in the audio band, as the aliased signal typical falls off 6dB/octave.

This is all very interesting, though a bit over my head. Let me ask another way: Considering only "typical" recording studio plug-in effects such as EQ and compression, is there a practical advantage to processing files at, say, 96 KHz rather than at 44.1 KHz? The reason I stress "practical" is because I just tried a simple test in Sound Forge using the Sonitus EQ plug-in bundled with Cakewalk SONAR I use, and I saw no added distortion or other artifacts when applying 10 dB boost at 1 KHz to a 1 KHz sine wave. All that happened is the tone got 10 dB louder.

For completeness, I created two files with the 1 KHz tone at -11 dB. Then I raised the volume of one file by 10 dB, and applied 10 dB of EQ boost with a Q of 24 to the other. The FFT displays of both files are identical, and neither has any added artifacts. Then I did the same test using 10 KHz both with volume boost and EQ at 10 KHz, and again the FFTs were identical showing nothing but the pure tone frequencies.

Edit: I forgot to mention the files were at a sample rate of 44.1 KHz.

--Ethan

This post has been edited by Ethan Winer: Jun 11 2012, 17:22


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drewfx
post Jun 11 2012, 19:11
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QUOTE (Ethan Winer @ Jun 11 2012, 12:18) *
This is all very interesting, though a bit over my head. Let me ask another way: Considering only "typical" recording studio plug-in effects such as EQ and compression, is there a practical advantage to processing files at, say, 96 KHz rather than at 44.1 KHz? The reason I stress "practical" is because I just tried a simple test in Sound Forge using the Sonitus EQ plug-in bundled with Cakewalk SONAR I use, and I saw no added distortion


Try repeating the test with white noise and some high frequency EQ and see if you see changes in the shape of the EQ curves.
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Ethan Winer
post Jun 12 2012, 17:46
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QUOTE (saratoga @ Jun 11 2012, 12:53) *
If your software is good, it should be upsampling when needed without you having to do it automatically.

That makes sense, and is about what I figured.

QUOTE (drewfx @ Jun 11 2012, 14:11) *
Try repeating the test with white noise and some high frequency EQ and see if you see changes in the shape of the EQ curves.

I can't use the same test with white noise. With a single sine wave I can achieve the same result with either a volume change or EQ. With noise there's no equivalent. I did, however, try boosting 10 KHz on a white noise file with a Q of 2 and again with a Q of 24. The resulting FFTs look as you'd expect in both cases.

So unless someone has an example that proves otherwise, I'll consider the notion that higher sample rates allow typical audio plug-ins to work better as just another audio myth.

--Ethan


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extrabigmehdi
post Jun 12 2012, 18:15
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QUOTE (Ethan Winer @ Jun 12 2012, 16:46) *
So unless someone has an example that proves otherwise, I'll consider the notion that higher sample rates allow typical audio plug-ins to work better as just another audio myth.


Hum, then what's the point of cd remastered at 96khz 24 bit ? (usually advertised on old classical titles).
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Posts in this topic
- Ethan Winer   Are high sample rates better for DSP?   Jun 10 2012, 20:13
- - knutinh   The higher the sample-rate, the better any approxi...   Jun 10 2012, 20:46
- - lvqcl   Here is an example of such filter (with explanatio...   Jun 10 2012, 20:56
- - benski   Yes, many filters work better with higher sampling...   Jun 10 2012, 21:17
|- - Ethan Winer   QUOTE (knutinh @ Jun 10 2012, 15:46) The ...   Jun 11 2012, 17:18
|- - saratoga   If your software is good, it should be upsampling ...   Jun 11 2012, 17:53
|- - drewfx   QUOTE (Ethan Winer @ Jun 11 2012, 12:18) ...   Jun 11 2012, 19:11
|- - Ethan Winer   QUOTE (saratoga @ Jun 11 2012, 12:53) If ...   Jun 12 2012, 17:46
|- - extrabigmehdi   QUOTE (Ethan Winer @ Jun 12 2012, 16:46) ...   Jun 12 2012, 18:15
- - xnor   Many EQs use simple bilinear-transformed filters (...   Jun 11 2012, 01:37
- - Woodinville   In addition to the warping one sees in a bilinear ...   Jun 11 2012, 01:46
- - extrabigmehdi   That's interesting, so basically if you want ...   Jun 11 2012, 02:30
- - bandpass   QUOTE (knutinh @ Jun 10 2012, 20:46) The ...   Jun 11 2012, 08:00
|- - knutinh   QUOTE (bandpass @ Jun 11 2012, 09:00) Tru...   Jun 11 2012, 08:30
- - bandpass   From a practical perspective, a particular effect/...   Jun 11 2012, 09:59
|- - knutinh   QUOTE (bandpass @ Jun 11 2012, 10:59) ......   Jun 11 2012, 11:55
- - greynol   I know the unofficial mantra around here is all th...   Jun 12 2012, 17:59
|- - Ethan Winer   QUOTE (greynol @ Jun 12 2012, 12:59) You...   Jun 12 2012, 19:35
|- - drewfx   QUOTE (Ethan Winer @ Jun 12 2012, 14:35) ...   Jun 12 2012, 20:29
|- - saratoga   QUOTE (Ethan Winer @ Jun 12 2012, 14:35) ...   Jun 12 2012, 21:12
|- - Ethan Winer   Thanks Drew for some hard evidence. Can you explai...   Jun 12 2012, 22:46
||- - benski   It's mostly that the shape (aka Q) is going to...   Jun 12 2012, 23:39
||- - drewfx   QUOTE (Ethan Winer @ Jun 12 2012, 17:46) ...   Jun 13 2012, 01:52
||- - andy o   I'm guessing these are the reasons why A/V rec...   Jun 13 2012, 03:27
|||- - Arnold B. Krueger   QUOTE (andy o @ Jun 12 2012, 22:27) I...   Jun 25 2012, 13:10
|||- - Woodinville   QUOTE (Arnold B. Krueger @ Jun 25 2012, 05...   Jun 27 2012, 21:59
||- - Ethan Winer   QUOTE (drewfx @ Jun 12 2012, 20:52) The 1...   Jun 13 2012, 19:55
|- - Woodinville   QUOTE (saratoga @ Jun 12 2012, 13:12) QUO...   Jun 13 2012, 01:22
- - greynol   Have you read the responses to your topic? I want...   Jun 12 2012, 19:42
- - greynol   As for the "it's best to record at 96kHz ...   Jun 13 2012, 00:53


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