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RE: One Comment, Two Questions

Years ago anybody trying to implement their own digital filter either had to design a custom chip (very expensive) or write software for DSP (digital signal processor), less expensive but inefficient.

With the advent of modern FPGAs its much easier to do your own custom filter. An FIR filter in an FPGA is not that complicated. The fun part is in figuring out exactly which filter function to use.

The problem is that we don't really know exactly what to optimize for. There is no equation that will design a filter that "sounds best". What happens is you have a hypothethis about what makes it bad or good, you design a filter that implements that (or DOESN'T implement it), then you listen. Repeat many times.

And to complicate things different people cannot agree on what constitutes the best tradeoff. I've been doing this trying different filters bit for several years now and have had several occasions where I had a group of people listening to the results. I would play a certain filter that I happened to like, and several of the listeners would agree that this was an improvement. But invariably one person whould respond with "thats awfull, what did you do to the sound?" So what do you do? Come up with the filter YOU like the best, or use the one with the broadest appeal of your test audience, or ...?

Then there is the issue of do you use the same filter for all sample rates? The big tradeoffs are for 44.1 since it is so close to the audio band. Does it make sense to use the same filter at 96 or 192? maybe not. I don't think there has been a lot of exploration of this aspect.

John S.

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