The VRC7 outputs significantly louder signals than any other Famicom sound chip. That's why you need to be careful with the volume values you use for it. Anything above 12 (C) is risky: not only it will completely drown out the 2A03, but it will likely result in clipping if you play your module in an accurate emulator (or the real hardware).
Actually, in terms of its absolute power output the VRC7 volume is sort of a little low,but the 2A03 audio return through the VRC7 cartridge is significantly attenuated to compensate. What Famitracker does is actually very accurate in this respect, though it's not doing it for that reason. The overall output volume is arbitrary, not something worth emulating.
The reason Famitracker drops the 2A03 volume when using VRC7 is to make headroom to avoid clipping when using everything at full volume. VRC7 is loud relative to the 2A03, and has a wide range, so the options are:
1. make everything quieter
2. make 2A03 quieter when using VRC7
3. have massive clipping when using VRC7
Though, jrlepage has reported clipping when the VRC7 is used at max volume. I don't think any emulators currently attempt to duplicate this behaviour. (NSFPlay will clip at high volumes, but that's not an attempt at VRC7 fidelity, merely a practical issue. So, it uses a compromise between options 1 and 3, where Famitracker uses option 2.)
I never liked how the triangle got crunched and noisier with the VRC7. It's almost as if the signal-noise-ratio is worse, or is that just what happens when you make such a "steppy" waveform quieter? In case of the N163 I can see that happening but why would that happen with the output for a computer soundcard with at least 16 bits of depth? Don't tell me there's no way to lower the volume without significant quality loss.
Alright. I made a very half-assed image showing a period of the triangle in 4 possible states (No VRC7, delta counter = 0; No VRC7, delta counter = 127; VRC7 on, delta counter = 0; VRC7 on, delta counter = 127) The zoom is a bit different ineach one but you can see how the little spikes at the beginning or the end of a step get more emphasized when the VRC7 is active.
The order in which you hear the waveforms in the recording is the same as in the parentheses. You can hear how there's a slight electric buzz added to the second and the third one, and the last one is just...what the hell?
P.S.:I had to post it as a split up .rar file to avoid having to use a lossy compression method.
za909, there should not be a strong timbre difference like that between Z00/Z7F, and with VRC7 it should be identical (just quieter). There should be a very subtle difference between Z00/Z7F due to the nonlinear output, but that's it.
I highly suspect that you have Famitracker set to output 8-bit sound instead of 16-bit.
I have confirmed the VRC7 clipping behaviour and that will be properly emulated at some time, as songs with louder volumes are useless when played back on the real hardware. Once that's added, I can probably remove the attenuation from 2A03 as well.
za909 wrote:
I never liked how the triangle got crunched and noisier with the VRC7. It's almost as if the signal-noise-ratio is worse, or is that just what happens when you make such a "steppy" waveform quieter? In case of the N163 I can see that happening but why would that happen with the output for a computer soundcard with at least 16 bits of depth? Don't tell me there's no way to lower the volume without significant quality loss.
It seems some bits are missing, probably a calculation error somewhere.
