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FamiTracker
I have been wondering how this works after experimenting with FamiTracker's sound settings. Since the beginning, I've always had FT's filtering settings at 20 Hz for bass and 20000 Hz with -0 dB damping for treble, which actually doesn't impact on sound at all as I've noticed. However, I grabbed an 8-channel Namco 163 module and I started listening to it and it gave me headaches after listening for half an hour due to the multiplexing hiss frequency (15000 Hz), which was totally unfiltered.
I tweaked my sound settings to try to filter this high frequency but I didn't have much success, probably because I don't exactly know how it works. I set the treble filtering to 15000 Hz with -90 dB damping and the hiss got a bit softer but I still noticed it. Tried with 12000 Hz and it was softer, 10000 Hz and it was softer too, but I still felt the high frequency blasting through the headphones. Finally, I tried 20 Hz and -90 dB damping and I don't notice it at all but the sound is a bit muffled.
Well, rather than getting a solution for this, I'm more interested in knowing how the filtering mechanism works. I've noticed enormous differences when using the bass filtering, but I haven't when using the treble filtering options.
What impact will have the frequency and damping settings on the output sound? Does this cap all the frequencies above the specified one or does it just make them quieter?
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The purpose of filtering is to allow some tuning for making the sound more similar to how it was reproduced on TV's back when the NES was popular, which usually had speakers with limited bandwidth. Filtering is a part of the Blip_buffer library that is used for synthesization, you can find information about that here: [url=http://code.google.com/p/blip-buffer/source/browse/trunk/notes.txt]http://code.google.com/p/blip-buffer/source/browse/trunk/notes.txt
But yeah there is some kind of issue with treble filtering, since -90dB would obviously render the frequencies above the limit impossible to hear, the actual filtering is nowhere near that. I don't know if it's the library itself or me using the library, I haven't investigated that.
Okay, I read the document, there were some things that I understood better after reading it. Also, I didn't know the purpose of the filtering settings was to make the sound more similar to that of the TV speakers. Hope you can find what's wrong with the treble filtering.
Thank you!
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I found that setting it to about 7000 Hz and -70 db was suitably like the filter in a TV's RF demodulation process. It was about the right setting to make it sound "like it would have sounded" on a TV.
I prefer the default setting though, because it's really close to what the NES' RCA output sounds like, which doesn't have such a strong lowpass like going through RF.
By the way, the damping in blargg's library says it is a logarithmic rolloff from -0db at the specified cutoff to the specified db at the nyquist frequency. This means that if the cutoff is high, changing the db might be a pretty subtle thing. There are a lot of limits to what it can do, I think, due to the nature of how it does the bandlimited synthesis.
I'll play around with those settings more often, so I can know how the sound gets affected with them. I'll try 7000 Hz and -70 dB now.
I had an NES clone of sorts during my childhood but I don't remember how it actually sounded on the TV, so maybe changing the filtering for a while will give me a rough idea of how it was.
I have a question though: I've understood that the filtering process is done on the TV, but what about the console itself? Does it do any filtering process prior to outputting sound?
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I understand. There's nothing else I need to know for now, so thanks for your explanations.
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