2013/4/20 Justin Chudgar <justin at justinzane.com>: > https://github.com/justinzane/pulseaudio Sorry for the delay with the answer. I was really busy at work, and will be very busy for at least two more weeks due to a new employee who needs guidance duing his initial work period. Still, here is the review. 1. I don't like the fact that the interface to construct a biquad filter (i.e. to calculate the proper coefficients) and the interface to do the filtering given the coefficients are in the same file. The current interface is good only for crossover filters and similar tasks. It is too limited for tasks that may arise in the future (e.g. replacement of the current 5.1-to-headphones filter with IIR would probably result in a good speedup, but a completely custom filter, not Butterworth, and not constructed according to any common cookbook formula). So let's not try to guess what the general interface would be, but let's move the current pa_biquad_calc_factors function to some less generic location, relevant only to Butterworth filters and LR crossovers. 2. Please remove options to create a high-shelf or other types of filters not relevant to your current work. They can be introduced when needed. 3. Please remove code that calculates coefficients for non-LR4 filters. It cannot be tested (because pa_biquad_chunk_4 assumes two stages) => it is useless now. Again, this can be introduced together with the first user. 4. My previous comment about an allpass filter being an invalid optimization has been ignored. Once again, the output of an allpass filter is not in phase with the output of a lowpass or highpass filter of the same order. So you cannot use it. For allpass channels, please use the sum of outputs of lowpass and highpass filters instead. I have not otherwise tested the correctness of the code and have not investigated what has been plotted. -- Alexander E. Patrakov
