It should not be circular buffer.
Could you explain meanings of "fade in", "fade out", "splice in", and
"splice out" ?


‫בתאריך יום ו׳, 15 במרץ 2019 ב-0:14 מאת ‪robert bristow-johnson‬‏ <‪

> ---------------------------- Original Message ----------------------------
> Subject: [music-dsp] pitch shifting vs sample rate
> From: "Alex Dashevski" <alexd...@gmail.com>
> Date: Thu, March 14, 2019 2:55 pm
> To: music-dsp@music.columbia.edu
> --------------------------------------------------------------------------
> >
> > Let's assume we have recorder buffer(input) and playback buffer(output)
> > with the same size.
> > I sample input signal at 8Khz and output signal at 9Khz.
> > My question is:
> > Why isn't it equivalent to pitch shifting ?
> >
> well, you didn't say how the samples in the playback buffer are defined.
> let's say that you are simply copying the input buffer to the output
> buffer.  or, even simpler, let's say that the input buffer and output
> buffer are coincidental, the same block of memory with two different points
> writing into it and reading out of it.  and let's say that these buffers
> are *circular* FIFO buffers.
> so, the output pointer advances 9 samples in the same amount of time that
> the input pointer advances 8 samples.  that would be pitch shifting, but
> you would have a click in the output every time the output pointer
> overtakes and passes the input pointer.  a good pitch shifter would fade
> out the signal from the output pointer before it catches up to the input
> pointer and would fade in the signal from another output pointer that is
> farther behind.  and would continue to do this.  once the signal is
> completely faded out, that output pointer is discarded and the fade-in
> output pointer (that was farther behind) becomes the nominal output pointer
> (which is still advancing 9 samples in the time the input pointer advances
> 8 samples).  when that gets too close behind the input pointer, we do this
> again and begin cross-fading to the signal further behind.
> a better pitch shifter would make sure that the new, fade-in output
> pointer is pointing to the waveform that looks similar to the fade-out
> output pointer.  this is what pitch detection is good for.  so when extra
> audio is spliced in (for up-shifting) or audio is spliced out (for
> down-shifting), you want ideally that an integer number of periods of the
> audio tone is spliced in or out.
> --
> r b-j                         r...@audioimagination.com
> "Imagination is more important than knowledge."
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