Detecting spectral envelope

Hi,

I'm using the most common audio pitch shifting algorithm via FFT. It works
fine, but not for shifting / keeping formants, especially for vocals. Do
you have some links for well working algorithms/ideas for detecting
spectral envelope used for this purpose?

I tried several ways and ended with an exceptionally simple thing - just
some moving average of a magnitudes of each FFT block. 

Thanks in advance.

On Dec 19, 10:17&#4294967295;am, "jungledmnc" <jungledmnc@n_o_s_p_a_m.gmail.com>
wrote:
>
> I'm using the most common audio pitch shifting algorithm via FFT.

how do you know what is the most common audio pitch shifting alg?  i
would be interested, since i haven't done the research of the market
nor digging in and reverse engineering the common pitch-shifting algs.

my guess might be that Autotune is the most common audio pitch
shifting alg.  i don't think it's a frequency-domain method, i think
it's a time domain method.  if they use the FFT for anything, it's not
that it's in the signal processing chain

> It works
> fine, but not for shifting / keeping formants, especially for vocals. Do
> you have some links for well working algorithms/ideas for detecting
> spectral envelope used for this purpose?

do you know about the old Digitech Vocalist?  it's a time-domain alg
(so no FFT) based on a paper by Keith Lent in Computer Music Journal
in 1989.  i did an analysis of it in 1993 and 1995 in the AES
Journal.  want a pdf copy?  it's not frequency domain and needs a good
pitch detector, so even without FFTing (and iFFT back) the pitch
detector is not a low computational burden.

but it retains the formant locations (the spectral envelope) without
going into the frequency domain.

> I tried several ways and ended with an exceptionally simple thing - just
> some moving average of a magnitudes of each FFT block.

sounds about as good as anything.

> Thanks in advance.

FWIW.

r b-j

Sorry, I wasn't explaining myself correctly - I meant phase vocoder using
FFT. I think it is the most used one. Time domain methods usually don't
work very well, especially with aperiodical signals (which polyphonic
usually are and vocals aren't so good either). I mean, for telephony and
stuff it may work, but for music, I don't really think so.

It is also quick common to "shift" formants by some amount, so it is needed
to be able to extract the spectral envelope somehow.

jungledmnc

>On Dec 19, 10:17=A0am, "jungledmnc" <jungledmnc@n_o_s_p_a_m.gmail.com>
>wrote:
>>
>> I'm using the most common audio pitch shifting algorithm via FFT.
>
>how do you know what is the most common audio pitch shifting alg?  i
>would be interested, since i haven't done the research of the market
>nor digging in and reverse engineering the common pitch-shifting algs.
>
>my guess might be that Autotune is the most common audio pitch
>shifting alg.  i don't think it's a frequency-domain method, i think
>it's a time domain method.  if they use the FFT for anything, it's not
>that it's in the signal processing chain
>
>> It works
>> fine, but not for shifting / keeping formants, especially for vocals.
Do
>> you have some links for well working algorithms/ideas for detecting
>> spectral envelope used for this purpose?
>
>do you know about the old Digitech Vocalist?  it's a time-domain alg
>(so no FFT) based on a paper by Keith Lent in Computer Music Journal
>in 1989.  i did an analysis of it in 1993 and 1995 in the AES
>Journal.  want a pdf copy?  it's not frequency domain and needs a good
>pitch detector, so even without FFTing (and iFFT back) the pitch
>detector is not a low computational burden.
>
>but it retains the formant locations (the spectral envelope) without
>going into the frequency domain.
>
>> I tried several ways and ended with an exceptionally simple thing -
just
>> some moving average of a magnitudes of each FFT block.
>
>sounds about as good as anything.
>
>> Thanks in advance.
>
>FWIW.
>
>r b-j
>