Re: [ecasound] Samplerate fascism?

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Subject: Re: [ecasound] Samplerate fascism?
From: Kai Vehmanen (kaiv@wakkanet.fi)
Date: Tue Nov 02 1999 - 20:32:10 EET


On 2 Nov 1999, Arto Hamara wrote:

>>> card (sb pci128) actually _does_ work, but supports samplerates one
>>> lower than standard (ie. 44099, 22049 etc), which ecasound happily
>> I hope other soundcard manufactures don't have similar habits
>> (of course 12345 means 22050 samples per second! :)) Of course you
> OSS Programmer's Manual states:
[...]
> The application should check the returned frequency and to compare it
> * with the requested one. Differences of few percents should be ignored
> * since they are usually not audible.

Differences of few percents!??! Aaarrggh (second arrgghh today,
doesn't look good ;))! Let's start with...

From the Linux audio quality HOWTO:
--cut--
The Multiple Soundcard Myth

Many people attempt to get more than two simultaneous inputs or
outputs by putting more than one cheap soundcard in their system. This
can be made to work, but there is a potentially large problem: Each
soundcard derives its sampling rate from a crystal oscillator clock.
The clocks in the two soundcards will inevitably not be synchronized.
You might think that 44,100 Hz is always exactly 44,100 Hz, but sadly,
it's not. As a result, the sound from one soundcard will gradually lag
farther and farther behind the sound from the other soundcard. If
there's any sound common to both cards, you may even get weird phasing
effects.
--cut--

So even differences smaller than 1Hz cause a lot of problems! Now if
the difference is 1Hz and we record 5 minutes of cd-quality audio,
there would be a 6.8ms error (in the end of) resulting output files.
So already with a 1.00002% difference in sample rate we get really
bad results. So "differences of few percents" is" is just _unacceptable_.

> So there. (OSS Program of the Month, alright ;))

Well, not for long... unless ecasound is re-elected. :)

>> Well, yesterday I spent the whole day working on ecasound and eventually
>> got it to compile... but as expected: no sound. Aarggh! It appears
> Hey, kinda like my soundcard. =)

Hah, I managed to find the bug! Now I can start testing the new
effect/dsp code!

--
Kai Vehmanen <kaiv@wakkanet.fi> -------- CS, University of Turku, Finland
 . http://www.wakkanet.fi/ecasound/ - linux audio processing
 . http://www.wakkanet.fi/sculpscape/ - ambient-idm-rock-... mp3/ra/wav


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