Commander X16 audio capabilities

picosecond · Post by **picosecond** » Wed Feb 03, 2021 9:07 pm

1 hour ago, BruceMcF said:

IIRC, VERA is like the Gameduino 1 in running on a 25MHz external clock and 50MHz internally, so the "8Mhz" option for the 65C02 PHI2 frequency is really 8.33MHZ, 25Mhz/3.

Probably not. I don't remember comments describing how Vera clocks are generated, but it appears PHI2 is generated from its own 8MHz crystal oscillator.

xanthrou · Post by **xanthrou** » Thu Feb 04, 2021 7:57 am

How would YM2151 rival YM2612 and YM3812?

BruceMcF · Post by **BruceMcF** » Thu Feb 04, 2021 6:11 pm

21 hours ago, picosecond said:

Probably not. I don't remember comments describing how Vera clocks are generated, but it appears PHI2 is generated from its own 8MHz crystal oscillator.

Oh, you kids & your new fangled "working eyesight". It does indeed appear to be working that way.

StinkerB06 · Post by **StinkerB06** » Sat Feb 06, 2021 12:32 am

Has the VERA PSG's noise LFSR algorithm been revealed yet? It's not implemented in the emulator's PSG code as far as I'm aware.

m00dawg · Post by **m00dawg** » Sat Feb 06, 2021 12:36 am

From what I understand, we won't be getting LFSR support on the VERA, at least currently. The emulator DOES have noise though - I use it in my (bad) Bad Apple cover tune for Command Tracker (a tracker I'm working on loosely based on Impulse Tracker). The noise is...well it's the noise we got if not the noise we want ?

StinkerB06 · Post by **StinkerB06** » Sat Feb 06, 2021 1:43 am

1 hour ago, m00dawg said:

From what I understand, we won't be getting LFSR support on the VERA, at least currently. The emulator DOES have noise though - I use it in my (bad) Bad Apple cover tune for Command Tracker (a tracker I'm working on loosely based on Impulse Tracker). The noise is...well it's the noise we got if not the noise we want ?

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.

m00dawg · Post by **m00dawg** » Sat Feb 06, 2021 1:46 am

Oh well that would be lovely if so! I also heard Lorin confirm there were no more changes to the VERA but maybe if it's already in there....

xanthrou · Post by **xanthrou** » Sat Feb 06, 2021 6:21 am

On 2/4/2021 at 8:11 PM, BruceMcF said:

Oh, you kids & your new fangled "working eyesight". It does indeed appear to be working that way.

Just wanna ask, how would YM2151 rival YM2612 and YM3812?

BruceMcF · Post by **BruceMcF** » Sat Feb 06, 2021 11:27 am

4 hours ago, xanthrou said:

Just wanna ask, how would YM2151 rival YM2612 and YM3812?

Don't know much more than is on the Wikipedia machine. The OPN2 (2612) and OPL2 (3812) both have more channels than the OPM, and the OPN2 has more similar FM synthesis ... the OPL2 is a two-operator FM synth, while the OPM and OPN2 are four operator synths. All three have sine wave based wave forms, but AFAIU, the OPL family are more complex ... there is a sine wave with the negative part clipped, one with the negative part to inverted to positive for a pseudo triangular wave form and one with the Senate he wave inverted and only the rising parts, for a pseudo sawtooth. Also the OPL family have dedicated percussion channels.

So the YM2512 is more like the 2612, but fewer channels, but AFAIU, wthout the low frequency sine wave oscillator or the simple PCM channel.

StinkerB06 · Post by **StinkerB06** » Sat Feb 06, 2021 4:08 pm

4 hours ago, BruceMcF said:

So the YM2512 is more like the 2612, but fewer channels, but AFAIU, wthout the low frequency sine wave oscillator or the simple PCM channel.

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.