[Openal] Playback rate inaccuracies

[CVOGELSANG at creativelabs.com]

>> 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
>else entirely?

This means that when playing back source data at let's say offset 7.121
that to compute the actual
output data 7 or 8 source data points are being used. Basically, an 8th
order interpolator, which has
a much better frequency response than a simple 1st order (linear)
interpolater, which acts more like a low
pass filter. Naturally, the actual algorithm how to derive the output data
from 8 input data points is not
public information.

-Carlo

-------- Notice --------
The information in this message is confidential and may be legally
privileged.  It is intended solely for the addressee.  Access to this
message by anyone else is unauthorized.  If you are not the intended
recipient, any disclosure, copying or distribution of the message, or any
action taken by you in reliance on it, is prohibited and may be unlawful.
If you have received this message in error, please delete it and contact
the sender immediately. Thank you.



|---------+------------------------------------>
|         |           Ed Phillips <ed at udel.edu>|
|         |           Sent by:                 |
|         |           openal-admin at opensource.c|
|         |           reative.com              |
|         |                                    |
|         |                                    |
|         |           10/12/2005 01:38 PM      |
|         |                                    |
|---------+------------------------------------>
  >--------------------------------------------------------------------------------------------------------------|
  |                                                                                                              |
  |       To:       Garin Hiebert <garinh at cheesetoast.net>                                                       |
  |       cc:       OpenAL Mailing List <openal at opensource.creative.com>                                         |
  |       Subject:  Re: [Openal] Playback rate inaccuracies                                                      |
  >--------------------------------------------------------------------------------------------------------------|




Hi,

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

>> done).
>
> 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
else entirely?

Thanks,

             Ed

Ed Phillips <ed at udel.edu> University of Delaware (302) 831-6082
Systems Programmer III, Network and Systems Services
_______________________________________________
openal mailing list
openal at opensource.creative.com
http://opensource.creative.com/mailman/listinfo/openal