[LAD] Drift compensation document

Len Ovens len at ovenwerks.net
Fri Sep 1 18:25:47 UTC 2017


On Thu, 31 Aug 2017, benravin wrote:

>>> so in a longer recording the left track
> and the right may be two different lengths
>
> If the sound card is clocked from a  single crystal, both the channels will
> drift by the same amount right ? How each channel will drift apart ? Could
> you please elaborate it.

When using SRC to match sample rate on a stereo unit, the two channels 
need to be processed together. Some of the ac97 audio cards just plugged 
two SRC units inline with the digital audio. The card's crystal would have 
given two channels of 48k audio in sync, but after the SRC units that sync 
would be lost. I also have some not so nice things to say about the HD 
audio that replaced AC97, but sync is not one of them.

People seem to forget that no matter what most MP3s use as a sample rate, 
in the minds of the Intel and Microsoft engineers, 48k is (was) the 
standard. So all those MP3s on a windows system would have gone through a 
sample rate change from 44k1 to 48k on their way to the audio card.

Internal Audio inputs are designed for using things like skype, where 
quality doesn't matter. The bit depth may be 16 or more bits, but the 
audio circuitry in front of that is closer to the cassette tape than any 
mic preamp used in a studio (even a bedroom studio for playing around in).

--
Len Ovens
www.ovenwerks.net



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