Hi Danijel,
Hamming and Hann windows have the same frequency selectivity: both have the
main lobe at 4 bins wide. For most "smooth" windows the frequency resolution
is roughly reciprocal to the "effective" window size. So if you find one
window has a better resolution than another at same size, it's very likely
the result of its being bulky (compare Hamming with Blackman, for example).
Kaiser and Gaussian windows allow you tune the balance between the bulk in
time and the bulk in frequency. But we like Hamming and Hann, because they
are simple, and 4 bins main lobe seems a good compromise. To further slim it
down you'll need swell up the window, pushing it towards the rectangular -
and we all know what's lurking that way.
The differentiations are often related to estimating frequencies. Say you
have a sinusoid, if you differentiate it, it's amplified by its frequency.
This can be arranged properly with windowed DFTs and give fairly accurate
frequencies for the fundamental as well as harmonics, but prefers the window
be differentiable.
Best,
Xue
-----Original Message-----
From: Danijel Domazet
Sent: Thursday, January 24, 2013 12:54 PM
To: 'A discussion list for music-related DSP'
Subject: Re: [music-dsp] Overlap-add settings for pitch detection?
Thanks Alexander.
Thanks Xue.
Xue, you say:
" It rarely matters much which window function to use. Both Hann and Hamming
are good. But if your pitch detector does differentiations, Hann might be
the preferable one as it differentiates naturally at both ends."
I thought window types were crucial for frequency selectivity? What did you
mean by "if pitch detector does differentiations"?
Cheers,
Danijel Domazet
LittleEndian.com
-----Original Message-----
From: music-dsp-boun...@music.columbia.edu
[mailto:music-dsp-boun...@music.columbia.edu] On Behalf Of Wen Xue
Sent: Tuesday, January 22, 2013 4:31 PM
To: A discussion list for music-related DSP
Subject: Re: [music-dsp] Overlap-add settings for pitch detection?
Hi Danijel,
the choice of window size has much to do with what your pitched source is
like. Usually the window should be long enough to include plenty of cycles
to fight against noise, but short enough to finish before any dramatic pitch
change. So if the pitch is known to be stable, the window can be very long.
If not, the ideal window size will depend on how fast the pitch changes. For
periodical pitch modulation the "effective" frame size is expected to be no
more than 1/10 of the modulation period; so for a voice modulated at 6Hz the
"effective" window size should be 16ms or less. Here "effective" refers to
the central part of the window where most energy are located. The actual
window size will be slightly (1.4x~2x) longer.
The overlap rate is very often 1/2 of the window size. Higher overlaps are
more frequently used for synthesis than for analysis. Where time resolution
is critical you can reduce the window size locally.
It rarely matters much which window function to use. Both Hann and Hamming
are good. But if your pitch detector does differentiations, Hann might be
the preferable one as it differentiates naturally at both ends.
Xue
-----Original Message-----
From: Danijel Domazet
Sent: Tuesday, January 22, 2013 2:23 PM
To: music-dsp@music.columbia.edu
Subject: [music-dsp] Overlap-add settings for pitch detection?
Hi music dsp,
In order to implement accuarate pitch detection we are sending input signal
through Fourier analysis stage. Are there any recommended settings with
regards to:
- Window frame size?
- Window overlap factor?
- Window type (Hamming, Hann, etc.)?
Thanks.
Danijel Domazet
LittleEndian.com
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