Soundcard sample rates

Soundcard sample rates may not be what they claim.

I have been testing different brands of PC soundcards. 44100 and 22050 are two of the standard sample rates that most soundcards support. Of course all sample rates are only as accurate as the crystal oscillator on the soundcard, so when I found several soundcards with a 22050 sample rate that was high by 0.6%, I chalked it up to poor crystal accuracy, or maybe ceramic resonators. But then I checked the 44100 sample rate on those cards and found it to be right on. I was puzzled as to why the 44100 sample rate was not exactly double the 22050 sample rate. When I made more careful measurements, it appeared that the 22050 sample rates were really trying for 22200, which is a less common standard.

Does anyone know why they might do that (and not tell anyone!)

By the way, the soundcard sample rates were all tested by writing a custom program to generate an audio tone of a certain frequency based on the assumption that the sample rate was the nominal rate requested. The the audio frequencies were measured with NIST-traceable means.

Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott
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sountracks,

On some soundcards the 44100 and 22050 are exactly in a 2:1 ratio. But a few other soundcards are definitely more like 44100 and 22200. No, I did not try

11025. And yes, I was very careful about the measurements.

Robert Scott Ypsilanti, Michigan

Reply to
Robert Scott

On a sunny day (Tue, 11 Nov 2008 18:50:47 GMT) it happened snipped-for-privacy@dont-mail-me.com (Robert Scott) wrote in :

Are you sure you made no measurement error? I have done some 11025 to 44100 conversions on hour long video material sountracks, and the sound was still 100% in sync with the picture. Did you also test 11025? Such a large difference would create big AV sync problems.

Reply to
Jan Panteltje

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assumption

If you have requested the sample rate which is not directly supported by the sound card hardware, the Win32 API will do the resampling to the supported rate automatically, without any obvious indication. The integrated sound chipsets typically support for 44.1kHz in hardware; all other rates are actually made by the software resampling. Perhaps what you see is related to the resampling artifacts for your particular hardware/software combination.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

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Reply to
Vladimir Vassilevsky

Not sure if this is the cause of or a similar thing to your observation, but the Creative/Soundblaster/SBLive!/Audigy line has had at least one lawsuit concerning false claims the company has made about the products (that a certain model does 24 bits when in most situations it doesn't). Also, many or most of their models have some hardware sample-rate-coverter that changes whatever sample rate you're using (usually 44.1k) to 48k to do whatever processing it does (volume control/mixing?) and then back to 44.1k to go to the computer bus or to the D/A or wherever. Bizarre but true.

Why are you doing this? Do you want to find a good soundcard? If so, don't go with any of the "consumer" cards that come with computers or on PC motherboards. They're all quite crappy compared to what you can get for a few more dollars. Get at least the "semipro" type - the minimum would be the Audiophile 2496 (and old but good product, I've had one for many years) here:

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Here's a 'legacy' site (it's been around a long time and I don't know when the last time the author updated it) with lots of soundcard test data, both consumer and semipro/pro:

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Reply to
Ben Bradley

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