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# fdesign.polysrc

Construct polynomial sample-rate converter (POLYSRC) filter designer

## Syntax

d = fdesign.polysrc(l,m)
d = fdesign.polysrc(l,m,'Fractional Delay','Np',Np)
d = fdesign.polysrc(...,Fs)

## Description

d = fdesign.polysrc(l,m) constructs a polynomial sample-rate converter filter designer D with an interpolation factor L and a decimation factor M. L defaults to 3. M defaults to 2. L and M can be arbitrary positive numbers.

d = fdesign.polysrc(l,m,'Fractional Delay','Np',Np) initializes the filter designer specification with Np and sets the polynomial order to the value Np. If omitted Np defaults to 3.

d = fdesign.polysrc(...,Fs) specifies the sampling frequency (in Hz).

## Examples

This example shows how to design sample-rate converter that uses a 3rd order Lagrange interpolation filter to convert from 44.1kHz to 48kHz:

```[L,M] = rat(48/44.1);
f = fdesign.polysrc(L,M,'Fractional Delay','Np',3);
Hm = design(f,'lagrange');
% Original sampling frequency
Fs = 44.1e3;
% 9408 samples, 0.213 seconds long
n = 0:9407;
% Original signal, sinusoid at 1kHz
x  = sin(2*pi*1e3/Fs*n);
% 10241 samples, still 0.213 seconds
y = filter(Hm,x);
% Plot original sampled at 44.1kHz
stem(n(1:45)/Fs,x(1:45))
hold on
% Plot fractionally interpolated signal (48kHz) in red
stem((n(3:51)-2)/(Fs*L/M),y(3:51),'r','filled')
xlabel('Time (sec)');ylabel('Signal value')
legend('44.1 kHz sample rate','48 kHz sample rate')```

This code generates the following figure.

For more information about Farrow SRCs, see the "Efficient Sample Rate Conversion between Arbitrary Factors" example, efficientsrcdemoefficientsrcdemo.