Erik de Castro Lopo wrote:
>On Fri, 22 Apr 2005 19:48:47 +0200
>Olivier Guilyardi <ml@email-addr-hidden> wrote:
>
>
>
>>About vary speed : I could use libsoundtouch instead of libsamplerate,
>>but I'm not sure the former can compare to the later's quality.
>>
>>
>
>Last time I looked, libsoundtouch used linear interpolation for
>doing vary speed. Linear interpolation is evil. Here is a table
>from a talk I presented a the audio minconf attached the LCA.
>
>The table is for doing linear interpolation for sample rate
>converting from 44100 to 48000. The signal is a single sine wave
>at the frequencies in the left column. The right column is the
>measured signal to noise ratio at the output:
>
>
> 333 Hz & 146.0 dB \\
> 666 Hz & 115.8 dB \\
> 1332 Hz & 103.8 dB \\
> 2664 Hz & 49.8 dB \\
> 5328 Hz & 38.7 dB \\
> 10656 Hz & 28.4 dB \\
> 21312 Hz & 19.5 dB \\
>
>Linear interpolation is simply no damn good unless you are *positive*
>the maximum frequency in your source material is less that 0.06 of
>the sample rate. For any real world signal, this is simply not the
>case.
>
>S
>
Well, I agree with you that linear interpolation is not great, but
realisticaly, compare to the artefacts created by a standart
time-stretching algorithm, it is not that significant. It all depends on
the time-stretch algorithm, and soundtouch is using a wsola algorithm.
Having implemented and tested a WSOLA algorithm myself, I would say the
sample rate convertor has almost no impact compared to the artefacts of
WSOLA.
Cheers,
David
Received on Sun Apr 24 16:15:05 2005
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