I agree strongly with Jean-Marc here.
there are many signal processing examples where 2 x nyquist ("2x
oversampling") does a much better job . I do all my two way radio speech
processing at "2x", especially peak control, and speaker pitch
estimation (I try and tell the difference between a male and a female
speaker for multiband band-splitters for multiband AGC) .
*****
The 300Hz point is highly valid. Most CTCSS subtone filters would be
3dB down at 400Hz, 20dB at 300 , 30+ dB down at 250.
And of course those filters are cascaded in TX and RX.....
glen
On 11/03/2017 2:52 PM, Jean-Marc Valin wrote:
> On 10/03/17 06:12 AM, Jeroen Vreeken wrote:
>> One of the things that I noticed while testing was that the current
>> pitch estimation sometimes makes a mistake and ends up with twice the
>> real pitch. I also got the feeling (but no proof yet) it was worse with
>> samples with heavy filtering under 300Hz (e.g. to get rid of CTCSS tones).
>> So there might be some room for improvement there...
>
> Pitch doubling/tripling is a common problem in pitch estimation. I spent
> some time trying to avoid it as much as possible in the Opus (CELT)
> pitch detector. You might want to have a look just in case (haven't
> tested) it works better than the existing codec2 pitch detector. Some of
> the things I have found that can help (and that the CELT code does):
>
> 1) Upsampling the pitch correlation (2x) to get fractional time
> resolution. Even if that resolution isn't needed, it helps reduce pitch
> doubling).
>
> 2) Looking at fractions of the pitch period to find peaks. e.g. if the
> correlation at T/3 is almost as good as the one at T, then we pick T/3
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