Commander X16 audio capabilities

[BruceMcF]

2 hours ago, StinkerB06 said:

The YM2151 has more channels (8 versus 6). The YM2612 has only 6 channels and not 7, as the DAC shuts off the 6th FM channel. Both of these have 4 sine-wave operators per channel, and include 8 different ways of combining these operators together.



The YM3812 is a 2-operator chip that supports 3 more waveforms, and 9 channels. The chip could be switched into a mode which replaces the last 3 FM channels with 5 channels of unique percussion sounds controlled with the FM channels' patch registers. This means the chip can produce up to 11 channels of sound at once.

Thanks for that. The OPN2 (YM2612) is also a cost reduced chip, with the DAC built in, and the DAC is lower resolution than the one that partners with the OPM (YM2151).

[xanthrou]

On 2/6/2021 at 8:15 PM, BruceMcF said:

Thanks for that. The OPN2 (YM2612) is also a cost reduced chip, with the DAC built in, and the DAC is lower resolution than the one that partners with the OPM (YM2151).

So the DAC that Commander X16 uses would have clearer sound than the DAC in Genesis.

[BruceMcF]

6 hours ago, xanthrou said:

So the DAC that Commander X16 uses would have clearer sound than the DAC in Genesis.

How clear the sound out is coming out of the system is more than how clear the signal is coming out of the DAC, and I am certainly neither an audio engineer nor privy to the details of the audio processing after the DAC analog out pins, but AFAIU, it may have the opportunity to be clearer.

[m00dawg]

4 hours ago, BruceMcF said:

How clear the sound out is coming out of the system is more than how clear the signal is coming out of the DAC, and I am certainly neither an audio engineer nor privy to the details of the audio processing after the DAC analog out pins, but AFAIU, it may have the opportunity to be clearer.

I think it's a good point. My TX81z, despite having an arguably inferior FM chipset, to say the OPL3 stuff, it sounds fantastic! Likewise, when I modded my NES with an audio buffer (inspired by the Cmoy headphone amp) to bypass the PPU, it sounds pretty awesome. It's also why the FPGA'ing of old sound chips isn't necessarily the complete story and can be why virtual synths/VSTs, can sometimes sound thin.

Curious what the X16 will have here. I haven't seen the board close enough to know what sort of audio output stage it will have between FM and Vera (and I hope a potential audio in for routing audio from cards and things).

[Kalvan]

8 hours ago, m00dawg said:

Curious what the X16 will have here. I haven't seen the board close enough to know what sort of audio output stage it will have between FM and Vera (and I hope a potential audio in for routing audio from cards and things).

Well, from what I've seen of motherboard prototypes on YouTube videos, VERA and the YM2151-YM3012 combo (and the SAA 1099s that are about to go bye bye) are on opposite sides of the current motherboard design.  Any circuitry solution that corrals all the sound signals to and from the expansion ports and/or an external output jack will need its own circuit layer all to itself.

[BTTFdude]

On 2/5/2021 at 8:43 PM, StinkerB06 said:

But @Frank van den Hoef did confirm in another thread here that an LFSR is used in the hardware HDL. He didn't give any specifics though, like the LFSR's width and what taps it uses, or if it's shared or per-channel.

As someone who has been fascinated with LFSRs as of late, I really hope they don't go for anything "bare-bones", like something using only two taps, but I suppose that depends on the configuration.

Personally, I hope a 15-bit LFSR with taps 14 and 15 will not be used (as is found in the SN76489, NES 2A03, SPC700, Game Boy, etc). That algorithm doesn't really give the "whitest" output, and it's especially jarring to hear in Game Boy games where sound effects (e.g. explosions) constantly reset the noise's initial value, resulting in something more akin to a "fart sound" that you hear at the start of the waveform (and I don't mean the 7-bit mode).