[vorbis] Downsampling

[volsung at asu.edu]

On Sun, 27 Jan 2002, [UNKNOWN] ï¾ûï¾û wrote:

> It is commonly said here that if I want to make AM radio-quality
> stuff at very low bitrates, a good way is to downsample.
> I downsampled a song to 11025Hz mono and encoded with -q 0,
> the result is about 18kbps and is at least radio quality.
> The downsampler I used is from Edinburgh speech tools, named
> ch_wave.  `sox' performs terribly, so I didn't use it.

Downsampling is a tricky process.  One thing to note is that there are several
algorithms for doing downsampling in sox, and I think the worst sounding (but
the fastest) is used by default.  My preferred downsampling command is:

ox test.wav -r 11025 test-downsample.wav resample

You can also do:

ox test.wav -r 11025 test-downsample.wav polyphase

Very fast, but very bad results are achieved with:

ox test.wav -r 11025 test-downsample.wav rate


---
Stan Seibert

<p><p>--- >8 ----
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