Thanx Alex,
>From what I know, a vocoder work in frequency, and analyse the signal.
Resampling just add/delete samples from the original so that played at a
different samplig freq, it will sound (nearly) the same.
But if you resample and play at the same sampling freq, the pitch will be
different...
So what I need would be something to change the pitch and not the sampling
freq (or better the duration of the sample and no pitch difference)
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Thursday, September 14, 2000 4:33 PM
Subject: RE: [MP3 ENCODER] Time-stretching (off topic)
| Howdy Steve,
|
| > Does anyone know a good technic/routine to time-stretch a
| > buffer of audio data
| > (mono channel) ?
|
| Assuming that you want to keep the pitch the same, phase vocoding comes to
| mind. This is an old speech processing trick (thus the vocoder) for
| shifting pitch without changing speed or vice versa. Grep around on the
| web, and if you don't find anything, I can maybe come up with some
| references. I'm sure there must be other (more modern) solutions.
|
| > Is it better to resample the data according to the
| > time-stretching ratio or
| > is there some other/better technic ?
|
| I'm not sure whether phase vocoding is just another name for resampling or
| not - I suspect both terms are often used fairly freely. My general
| understanding of resampling is that it simply changes the effective
sampling
| frequency; but (for instance) doubling the number of samples and then
| playing back at anything other than double the rate will shift both pitch
| and speed. I could be wrong, though. I seem to recall that the process
| MIDI tone banks use to play different pitches from the same underlying
| sample (which is properly called interpolation?) is referred to as
| resampling as well. To say whether that's the same underlying algorithm
as
| phase vocoding or not, I'd have to read up a bit.
|
| Boy, can I hedge more than that?
|
| Hope that helps,
| Alex
|
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