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Topic: Vorbis sample rates (Read 9640 times) previous topic - next topic
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Vorbis sample rates

Pardon if this has already been asked (I couldn't find the relevant link).

libvorbis seems to preserve the input sample rate regardless of bitrate, when formats like MP3, AAC etc. downsample as necessary. Is this totally fine, or would an encoder benefit from integrated SRC for excessively high (>48kHz) sample rates or very low bitrates?

Vorbis sample rates

Reply #1
Probably not a bad idea.  You'll at least save a little bitrate, and avoid parts of the codec that are probably less well tuned.

Vorbis sample rates

Reply #2
Might not make as much difference as you think in file size.  Just to try it I converted to OGG a 192/24 recording 207 meg in size.  Recorded with DPA mics flat to 40 khz.  There just isn't that much info at upper frequencies.  I had previously resampled the recording to 44/16.  The OGG at highest quality for the 192 file ended up being 12.1 meg and the 44/16 file was 10.7 meg in size.  My guess is the stuff below 20 khz was encoding the same one way or the other, and with the reduced level above 20 khz it only took 1.4 more meg to encode it.  Doing the same to a 96/24 version ended up as 11.4 in OGG format.  Only .7 meg larger than 44/16.

So unless the lower file size is critical you likely don't loose much just letting it use the higher sample rate.  Also from mid quality settings and lower OGG rolls frequencies off sharply above 20 khz and the files sizes are even closer together.

Vorbis sample rates

Reply #3
Is there anything about the input that would require a high sample rate?  Are you planning to use a high enough quality setting that high frequencies won't just be filtered out?  Unless there is some potential use for the extra samples, you might as well get rid of them.