# Applying a multistage filter to a signal, how?

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Paramonte on 7 May 2014
Considering the filter explained in the mathworks documentation centre:
Fpass = 0.11; Fstop = 0.12; Apass = 0.02; % 0.02 dB peak-to-peak ripple Astop = 60; % 60 dB minimum attenuation M = 8; % Decimation factor of 8 Hfd = fdesign.decimator(M,'lowpass',Fpass,Fstop,Apass,Astop);
Hm_multi = design(Hfd,'multistage')
Hm_multi =
Stage(1): Direct-Form FIR Polyphase Decimator
Stage(2): Direct-Form FIR Polyphase Decimator
Stage(3): Direct-Form FIR Polyphase Decimator
PersistentMemory: false
If my original signal supposedly sampled at 8KHz (want to dowsample it to 1KHz, thus M=8) how do apply the Hm_filter to the data for decimation. Apply the filter first and then decimate the filter output by 8? I note that the filter has three stages that would suggest applying it in a multi-stage manner. Thanks in advance! Para

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