HydrogenAudio

Hydrogenaudio Forum => Listening Tests => Topic started by: zohasaba on 2015-06-14 14:52:55

Title: anchor sound
Post by: zohasaba on 2015-06-14 14:52:55
hi

I want produce anchor from target sound, how can do it?

The standard anchor is a low-pass filtered version of the original signal with a
cut-off frequency of 3.5 kHz;

thanks
Title: anchor sound
Post by: xnor on 2015-06-14 15:47:57
If you have fdesign:
Code: [Select]
Fs = 44100;  % Sampling Frequency
N  = 2;     % Order
Fc = 3500;  % Cutoff Frequency

h  = fdesign.lowpass('N,F3dB', N, Fc, Fs);
Hd = design(h, 'butter');


Then you can filter(Hd, your_signal).


Otherwise you can calculate a biquad low pass filter like this:
Code: [Select]
w0 = 2*pi*fc/Fs;
alpha = sin(w0)/(2*Q);

b0 =  (1 - cos(w0))/2;
b1 =   1 - cos(w0);
b2 =  (1 - cos(w0))/2;
a0 =   1 + alpha;
a1 =  -2*cos(w0);
a2 =   1 - alpha;

b = [b0/a0 b1/a0 b2/a0];
a = [1 a1/a0 a2/a0];


You then filter with filter(b, a, your_signal). Q would be 1/sqrt(2) for butterworth.
Title: anchor sound
Post by: zohasaba on 2015-06-17 10:52:39
thanks for help

in mushra mention anchor made bellow instruction.

. The standard anchor is a low-pass filtered version of the original signal with a
cut-off frequency of 3.5 kHz;
The characteristics of the 3.5 kHz low-pass filter should be as follows:
fc = 3.5 kHz
Maximum pass band ripple = ±0.1 dB
Minimum attenuation at 4 kHz = 25 dB
Minimum attenuation at 4.5 kHz = 50 dB.
how can effect  Minimum attenuation at 4.5 kH z  and Minimum attenuation at 4 kHz  and  Maximum pass band ripple ?
Title: anchor sound
Post by: xnor on 2015-06-17 11:07:41
Oh, in that case you need to change the filter design quite a bit. Look up the documentation on filter design. You can specify pass- and stopband and attenuation etc.
Title: anchor sound
Post by: zohasaba on 2015-06-17 11:11:18
ok
I look at f design low pass filter,but I see one stop band in design.
I want use two mininmum attention mention at 4 kHz and 4.5 kHz.
how can this do?
Title: anchor sound
Post by: xnor on 2015-06-17 11:55:52
Depending on the filter type you'd just pick one of these for a lowpass and then increase the filter order if necessary to satisfy the other requirement.

Or just start with the cutoff frequency and fixed order which you then increase.