MiSTer FPGA Forum

I noticed that NES, TGFX16, Gameboy and MegaCD now have a setting "Audio filter - Custom" that can load files like the screen filters, but there are no files. Would anybody know what it does, where to get such filter files and which are recommended to make the respective system sound as original as possible?

Download LPF20000.txt, LPF2000_2tap.txt, LPF2000_3tap.txt from https://github.com/MiSTer-devel/Main_MiSTer and put into filters_audio directory. I supose more filters will be available in the future.

Very cool feature! I'm guessing the files mentioned above are low-pass filters. My quick audio noob research says that the net effect is 'reducing high pitched noise'. Is this filter essentially dumbing down the range of whatever speakers you are using?

One of its intended uses is to reduce harmonics and artifacts which are generated by low-frequency sampling, especially when resampled at a higher but non-harmonic rate, and for beat frequencies by slightly-differing rates (i.e. SPDIF 48K of 44.1KHz CD audio).

Another one is that the original machines included such filters (although analog), so these are really trying to bring the audio back to what an original system sounded like, as much as possible.

MDFourier is being used to judge the outputs.

Jeruro wrote: ↑Mon Jun 22, 2020 6:00 pm Download LPF20000.txt, LPF2000_2tap.txt, LPF2000_3tap.txt from https://github.com/MiSTer-devel/Main_MiSTer and put into filters_audio directory. I supose more filters will be available in the future.

Interesting. In digital filter design, are "taps" in any way related to "poles" in analog filter design? The number of poles in an analog filter is a way of defining the slope of the filter, with one pole equal to 6dB per octave of attenuation past the cutoff point

Any update or source for these yet?

Anyone have any other example filters yet? Or a break down of what the values mean and what they do?

Phaedrus wrote: ↑Mon Sep 07, 2020 5:16 am Anyone have any other example filters yet? Or a break down of what the values mean and what they do?

I second the motion! A basic guide on MiSTer's audio filters would be awesome. I've been trying to actually increase the overall gain (instead of filtering out, more the opposite), but I only seem to end up with white noise or no sound. My crazy(?) goal is to try to match the semi-over amplification that some arcade DACs do

I mostly use the arcade filters. Audio frequencies above the selected filter frequency will be diminished (which is called a low-pass filter).

2nd order filters filter steeper than 1st order ones (24 dB/octave vs 12 dB), so the frequencies above the filter frequency will be diminished less gradually with the 2nd order filters. The 2nd order filters 'stronger'.

I mostly use the 4000Hz 2nd order ones for old bleepy cores (early eighties and below) and 8000Hz 2nd order ones for 16-bit cores, if needed.

There are some premade filters in the repo now so it's not just a useless feature anymore. Mostly useful for the harsh arcade sounds.