Tuesday, April 27, 2010

Ardour And Sample Rate-Quick Note-Linux Audio

In my AV Linux review of [data] I said this about Ardour.

My only other complaint about Ardour is that it does not cope well with imported audio that is of a different sample rate than the official rate of the session.
This agrees with the Importing Audio section of Ardour's FLOSS manual.
If the sample rate of the file you have chosen does not match the sample rate of the current session, Ardour colours the mismatched sample rate in red. If you try to import the file, Ardour will also warn you of the mismatched rate and ask you to confirm if you want to embed it anyway. If you do choose to embed the file in question, it will not play back at the sample rate it was recorded with, but rather at the sample rate of the current Ardour session. This will cause the sound to play at the wrong speed and pitch.
Well, that appears to not always be true and may have been a problem with that specific set-up. Today I tried it again and it worked fine. The screen shot below shows the results of what I did.

The sample rate for the session/project is 48kHz. The bottom two tracks are bounces/exports of the tracks above, one bounced out at 48kHz and one at 44.1kHz. When I imported them back in Ardour did flag the 44.1kHz file's sample rate in red but it does, in fact, play correctly.

Spectrum analysis of the two regions show that they are almost identical. The 48kHz region is slightly brighter, with most of the difference in the top octave of human hearing. This is consistent with more high frequency information being preserved in the encoding of the higher sample rate file (as it should be) but both of them playing correctly after being imported back in. This, of course, is a good thing but contradicts the FLOSS manual.

As a further test I did a third export at 88.2kHz.

Again the sample rate was flagged in red. Again the file played at the correct pitch at speed but was very loud and clipped.

Like other free/open source software Ardour has a community surrounding it. I have started reading two of the Ardour mailing lists and other internet venues where the community lives and interacts. I will keep you posted as I learn more about this wonderful application.

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