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Hello,

I am looking for a way to obtain the lowest group delay.
The specifications are;

Lowpass filter
fpass=1kHz with 3dB Ripple
fstop=4kHz 
Attenuation 60dB (between 4kHz and 20kHz or between 4kHz and 97.5kHz)
with sampling frequency: 195kHz
up to 1kHz linear phase and constant group delay (needed)

If I use Generalized Equiripple FIR filter of Matlab fda toolbox, the
minimum order is 115 (so 57.5 Tabs delay)

Is it possible to obtain a new filter which has a delay less than 57.5
Tabs for the given specifications?

Best Regards

Gokhan

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Gokhan-

> I am looking for a way to obtain the lowest group delay.
> The specifications are;
>
> Lowpass filter
> fpass=1kHz with 3dB Ripple
> fstop=4kHz
> Attenuation 60dB (between 4kHz and 20kHz or between 4kHz and 97.5kHz)
> with sampling frequency: 195kHz
> up to 1kHz linear phase and constant group delay (needed)
>
> If I use Generalized Equiripple FIR filter of Matlab fda toolbox, the
> minimum order is 115 (so 57.5 Tabs delay)
>
> Is it possible to obtain a new filter which has a delay less than 57.5
> Tabs for the given specifications?

What is meant by "up to 1 kHz linear phase and constant group delay"?  Assuming this
means linear phase from dc to 1
kHz, you might try converting your FIR filter to minimum phase (MATLAB has a function to do
this).  This will reduce
group delay, but also make phase non-linear.  Possibly the phase response from dc to 1 kHz is
still acceptable.

-Jeff

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