# FIR Filter Design - from slope and cutoff frequency [duplicate]

I am stuck with the following design requirements for FIR filter:

1. Low-pass
2. -6dB @ 1.6kHz
3. Slope: 24 dB/octave.

Ideally I would like to get also FIR coefficients, but any help how to design this filter using MATLAB, ScopeFIR, ScopeIIR, or any other software/method that you may find useful will be appreciated.

Thank you.

• Just use the simple code I showed you as an answer to your other question, and choose a slightly lower cut-off frequency for the Butterworth design (so you get 6dB at 1.6 kHz instead of 3dB). What's the problem? – Matt L. May 12 '15 at 21:05
• You can modify your existing question instead of re-asking almost the same question. – hotpaw2 May 13 '15 at 6:33
• @MattL.Ok, I think I got 6dB at 1.6kHz by choosing lower cut-off frequency. But, Matt, can you show to me that the slope is 24dB/octave? I checked your plot (in MATLAB), and it seems that the curve is steeper than 24dB/oct. Am I missing something? Thank you. – Nebojsa May 13 '15 at 12:19
• @Nebojsa: The initial decay is about 24dB / octave. For higher frequencies it becomes steeper because the response decays to zero (i.e. $-\infty$ dB) at Nyquist. So the minimum slope is about 24dB / octave (close to the cut-off frequency) and then it increases. – Matt L. May 13 '15 at 15:48