[Openal] Playback rate inaccuracies
ed at udel.edu
Wed Oct 12 13:38:32 PDT 2005
On Wed, 12 Oct 2005, Garin Hiebert wrote:
>> It would be interesting to know what programs like Cubase, Cakewalk, Logic,
>> etc. do in this case. I use Cakewalk for music recording, and it does a
>> "calibration" with the audio hardware, which seems to determine what it
>> needs to do to keep recording and playback in sync, and as a result, keep
>> playback sounding just like the original recording sounded.
> They use ASIO, which internalizes syncing issues (corrects all system audio
> I/O to a master clock). I'm not sure if all sound cards support ASIO under
> Windows, but Creative's do and I suspect that most others do as well. ASIO
> isn't a 3D API, though...
Cakewalk can operate with drivers that support ASIO, WDM or MMSYSTEM type
of interface... and it seems to do a good job with MMSYSTEM drivers (for
example, Creative SBLive! drivers for Win98)... but maybe that depends on
the accuracy of the sound card record/playback clock. So, I'm not sure
what data the actual "calibration" feature is gathering and how it's using
it to correct record+playback offset (lag) and timing inaccuracy...
>> My guess is that it can be done without pitch-shifting - I've never noticed
>> the "artifacts" or "weirdness" that pitch-shifting would inevitably produce
>> when using Cakewalk (but I guess that doesn't really mean it's not being
> The quality of the resampling will depend on the card/driver being used.
> Creative cards have 7 (Live!) or 8 (Audigy, X-Fi) point interpolation,
> so there aren't noticeable artifacts. Most audio cards do linear
> interpolation, with more noticeable results.
What does that mean exactly? Do they take 7/8 points of data and "curve
fit" them so that a new set of samples can be calculated (based on the
curve function) at any location along the time-line (at the new sampling
rate)... or does it mean that 7/8 points are computed between each sample
(according to some algorithm) and the new sampling rate can simulated by
choosing from the original + interpolated samples? Or is it something
Ed Phillips <ed at udel.edu> University of Delaware (302) 831-6082
Systems Programmer III, Network and Systems Services
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