>> Long time FIR Designer user and a great fan. I’m currently on a project
>> were i need some fir filtering in the really low end. So obviously i am
>> getting high latency. Is there any chance you could insert the design of
>> warped FIR filters ? As i am reading they seem to be able to work in the
>> low end without the high latencies.
Good question. 🙂
FIR filter latency and length are not directly related. For example it’s possible to have a very long minimum-phase FIR filter – e.g. 20,000 taps – that goes very low in frequency and has little to no latency. In FIR Designer we have “length” and “delay” settings. If all the filters on the Mag Adjust and Auto Mag tabs are set to minimum-phase, then the FIR filter “delay” can be set to 0.
Traditional FIR filtering uses a single sample delay element between each FIR filter tap. Common warped FIR’s replace the each single sample delay with an all-pass filter that provides frequency-varying delay at each filter tap; i.e. longer delay at lower frequencies. Warped FIR’s are an implementation technique that reduces the number of FIR filter coefficients to reach lower frequencies; potentially yielding lower computation.
Implementing desired filter using a warped FIR method doesn’t inherently change the characteristics of the filtering – e.g. doesn’t change latency. Traditional and warped FIR’s do differ in frequency resolution. For an equivalent number of FIR filter taps, a traditional FIR filter has finer resolution at HF and lower resolution in the LF, whilst a warped FIR has finer resolution in the LF at the expense of coarser resolution in the HF.
I’m not aware of any general purpose or audio DSP’s that have warped FIR filter processing blocks ready to take FIR coefficients. If you know of one, please let us know. Warped FIR’s tend to be used in closed, proprietary or embedded systems.
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