[mirtoolbox] Re: mircepstrum delays
- From: Hendrik Schreiber <hs@xxxxxxxxxxxx>
- To: mirtoolbox@xxxxxxxxxxxxx
- Date: Tue, 12 Oct 2010 19:23:34 +0200
On Sep 24, 2010, at 13:46 , Olivier Lartillot wrote:
> Hi Hendrik and List,
>
> This is a very pertinent question. I propose to update the explanation of
> mircepstrum options in the User's Manual as follows:
>> mircepstrum(..., ‘Min', min) specifies the lowest delay taken into
>> consideration, in seconds. Default value: 0.0002 s (corresponding to a
>> maximum frequency of 5 kHz). This default value is not set to 0 s in order
>> to exclude the very high peaks confined in the lowest quefrency region:
>> these high peaks seem to come from the fact that the spectrum is a
>> non-centered signal, thus with high (quasi-)stationary energy. However, the
>> value can be forced to 0 using this ‘Min’ option.
>> mircepstrum(..., ‘Max', max) specifies the highest delay taken into
>> consideration, in seconds. Default value: 0.05 s (corresponding to a minimum
>> frequency of 20 Hz). This default value is not set to Inf in order to
>> exclude the very high peaks confined in the highest quefrency region: these
>> high peaks seem to come from the fact that the spectrum is a highly variable
>> signal, thus with high energy on its highest frequencies. However, the value
>> can be forced to Inf using this ‘Max’ option.
>
> Would this be correct and clear?
I have no idea, whether it is correct, but I can attest that it is clear.
This is mostly speculation as I haven't done any reading on this, but perhaps
one can also explain the min/max parameter by pointing to auto correlation.
When computing auto correlation the naive way (i.e. not using DFT), min/max
delay makes immediate sense. Now, Cepstrum is in a way a modified auto
correlation, therefore one might want to have the same 'tuning' parameters.
-hendrik
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