Re: [Tftb-help] TFRSCALO Parameters & Output Help Needed

[Eric Chassande-Mottin]

dear Yasemin,

the output matrix of tfrscalo should not have negative values
as it is a modulus square of a complex quantity. this is indeed
what i observe when computing

sig=altes(64,0.1,0.45); tfr=tfrscalo(sig); any(tfr(:)<0)
ans = 0

(this is taken from the example given in the online help).

it is likely that you are not using tfrscalo properly.

if you want to get further help, the easiest would be
that you post to this list a small example (like the above) that
reproduce the problem you have.

cheers,
eric

On Thu, 9 Oct 2008, Yasemin Gokce wrote:

> Dear Ladies and Gentleman,
>
> I have a question on the use of tfrscalo use. We are analyzing brain waves
> and we would like to use tfrscalo to compute the spectrogram (frequency vs
> time) from a time-amplitude signal.
>
> Our high-level understanding of the process is that we should be feeding the
> time-amplitude signal into tfrscalo. The out put is a 1-by-4 matrix. And the
> first value in the output is the magnitude squared of the wavelet transform.
>
>
> To normalize the values of the output matrix, we've been informed that we
> should scale down our values by a certain constant and then take the square
> root of the data. Apparently, for other researchers, this method works and
> they get a reasonable range that you might expect from brain wave data.
>
> However, we cannot take the square root of the values in our tfrscalo output
> matrix, because some values are negative. I was wondering
>
> 1) Is it possible for the output matrix of tfrscalo to have negative values?
> 2) If we feed tfrscalo a time( seconds) - amplitude (volts) signal, what are
> the units of the values in the output matrix?
>
> Best regards,
> Yasemin