[LAD] interesting blog post about syncing blender and ardour

Fons Adriaensen fons at kokkinizita.net
Fri Sep 25 17:18:26 UTC 2009

On Fri, Sep 25, 2009 at 12:06:38PM -0400, Paul Davis wrote:

> in 2.X, the resampling is done with very poor quality linear
> interpolation, so ardour can resample a pretty large number of tracks.

Are you sure ? I measured it today (using the manual varispeed)
and got some very strange results:

- large amounts of non-harmonic distortion, basically spectral
lines which are 46.9Hz apart (= Fs / 1024). 1024 was also the
period size.

- occasionally phase jumps, usually together with a single
  sample going to over 1e+15. Ardour's meter on one of
  the test tracks went up to +300dB while playing a 2Khz
  sine with +2% speed change.

None of this would be produced by linear interpolation.

> in 3.X, there are some choices about what type of interpolation to
> use. the underlying assumption here is that if the user wants ardour
> to varispeed (and note that the same code is used for
> scrubbing/shuttling too), then they do not care *much* about quality.
> this is not "sample rate conversion" in the traditional sense - its
> "resample so that we can stay in sync".

Still, there's no point in using any DAW if the result is not
recorded somehow and used later. So quality does matter.

> If a signal is recorded
> > with some speed error, and then played back with the same
> > speed error the result should be the original signal. Since
> > it will be resampled on playback it has to be resampled on
> > record as well, in the opposite direction.
> sure. however, i have no great interest in implementing this because
> from my perspective, the "errors" that occur when the timecode source
> is not sample clock synced are generally *not* repeatable, and thus
> attempting to support this would actually not accomplish the goal.

It would. Even if the record/playback errors are not the same, the
expected result depends on their ratio, even if that ratio is not
unity or constant.



Io lo dico sempre: l'Italia è troppo stretta e lunga.

More information about the Linux-audio-dev mailing list