How can I use fast FFT-based convolution to implement a LPF if the fast convolution requires a LPF?

Question

I\'m an experienced software engineer with some minor college DSP knowledge. I\'m working on a smartphone application to process signal data, such as from the microphone (sample

Answer 1

FFT based convolution is an optimization for when you need a low-pass with a cutoff frequency below the low-pass filter required for anti-aliasing before the sampling. e.g. 2 low pass filters, one in hardware, one in software. This is commonly done when the 2 low pass filters can create a given filter quality (passband flatness, etc.) better or cheaper than one hardware filter before the sampler, or if the sampler itself introduces noise (mostly) in the spectrum above the desired signal.