I am going to implement sound output filtering in DOSBox-Staging and I'm having trouble finding accurate information on the exact lowpass filters used in various Sound Blaster models. I've already tried to extract as much information from this forum as possible (with good results!), but there are still a few areas where I'm not 100% sure, so I'm asking for your help.

Below is my plan so far; it's mostly based on the awesome measurements made by @James-F. Where there were no measurements available, I tuned the filters by ear and looked at spectrum analyser readings. (Generally, I trust measurements first, then my ears and the analyser, then specs only as a last resort, as they're often wrong).

The ones marked by question marks were tuned by ear, so I'm a little unsure about those. To me, they all sound good and pretty close to real recordings, but I want to get this right so I thought it wouldn't hurt to ask you guys. If someone would be willing to record some white-noise from real hardware (especially for the OPL paths), that would be most appreciated!

Cheers!

PCM

For all models except the SB16, there's a zero-order-hold upsampling step to the 45454Hz DAC rate first (nearest-neighbour interpolation, basically).

• SB1.0 – 12dB/oct lowpass @ 3.8kHz
• SB2.0 – 12dB/oct lowpass @ 4.8kHz (?)
• SBPro1, SBPro2 – 12dB/oct lowpass @ 3.2kHz
• SB16 – brickwall lowpass @ half the SB mixer rate (with proper upsampling)

OPL

• SB1.0, SB2.0 – 6dB/oct lowpass @ 12kHz (?)
• SBPro1, SBPro2 – 6dB/oct lowpass @ 8kHz (?)
• SB16 – no filtering