Sound Chip?

Travis Bryant moore · Thu Jun 03, 2021 10:34 am

sorry for not reading the FAQ.

BruceMcF · Post by **BruceMcF** » Thu Jun 03, 2021 2:25 pm

9 hours ago, Travis Bryant moore said:

Was there a way to digitize auto and store it in a digital memory and convert back into analog sound? Say I ran a cd or 8 track into an analog to digital converter and stored it on a sd card and played it back though a digital to analog converter and maybe had the help with an amplifier? Or would such sounds be run by a Yamaha dx27? ... And could the DX24 play one audio channel or more than one like a voice but dymanically shift the voice to emulate an audio channel?

The thing about a keyboard synthesizer is that if you want to hit five keys at a time to play a chord, that means you need five channels. And if you want to have one key still fading while another key is being struck, they both need to have their own channel. So a "channel" is not like "front left, front right, back left, back right, bass" in a 4+1 surround sound but rather an electronically generated source of a particular tone.

So the DX 27 and DX 100 are the full sized and compact version of the same consumer level synthesizer. The DX21 is the higher end consumer version using the same chip but with more flexibility in how it uses it ... you could have different "instruments" in each half of the keyboard OR make an "instrument" from combining two different FM voices.

If the YM2151 does end up being in the finished CX16p, it will have even more flexibility ... if you want to be able to have five overlapping versions of one instrument, two overlapping versions of another one and an instrument that doesn't overlap, that can be programmed ... just as long as the total number of voices at one time is never more than eight. A lot of people who appreciate FM synths like the Bass 01 patch in the Yamaha presets, but other than that few people seem to like any of the other Yamaha presets and prefer patches that have been created by other people over the years.

Eight FM channels, 16 PSG channels and the PCM for waveforms that aren't effectively provided by the first two is a lot of flexibility in generating tunes in a chiptunes approach. But it's not focused on being a ".WAV" player, because that approach is bandwidth intensive for an 8bit system.

Travis Bryant moore · Post by **Travis Bryant moore** » Thu Jun 03, 2021 7:39 pm

So the Vera is that a full wave player or having one of those if I put a cd rom drive in the cx16 could I then listen to some beach boys music?

Elektron72 · Post by **Elektron72** » Thu Jun 03, 2021 9:39 pm

1 hour ago, Travis Bryant moore said:

So the Vera is that a full wave player or having one of those if I put a cd rom drive in the cx16 could I then listen to some beach boys music?

If you'd like to see what the VERA's PCM playback system is capable of, I would recommend watching this video.

BruceMcF · Post by **BruceMcF** » Fri Jun 04, 2021 12:32 am

4 hours ago, Travis Bryant moore said:

So the Vera is that a full wave player or having one of those if I put a cd rom drive in the cx16 could I then listen to some beach boys music?

That's the PCM, not the FM or the PSG. It would be using much more of the total processing power of the system to operate it that way than to generate sound in a chiptunes approach.

Travis Bryant moore · Post by **Travis Bryant moore** » Fri Jun 04, 2021 1:58 pm

Some of the higher kilohertz playbacks are good enough.

16 hours ago, Elektron72 said:

If you'd like to see what the VERA's PCM playback system is capable of, I would recommend watching this video.

ZeroByte · Post by **ZeroByte** » Sat Jun 05, 2021 4:15 am

Technically the VERA PCM is better than CD quality.

48KHz 16bit stereo.

However, like bitmap mode, turning all the options to max quality hits a wall where you really can’t feed it what it needs at those settings.

640x480 @8bpp won’t fit in VRAM. So you can have 640x480 OR 8bp, but not both.

48KHz 16bit stereo will fill 2MB quite quickly. (10 2/3sec roughly)

Travis Bryant moore · Post by **Travis Bryant moore** » Sat Jun 05, 2021 4:52 am

Quote

34 minutes ago, ZeroByte said:

Technically the VERA PCM is better than CD quality.

48KHz 16bit stereo.

However, like bitmap mode, turning all the options to max quality hits a wall where you really can’t feed it what it needs at those settings.

640x480 @8bpp won’t fit in VRAM. So you can have 640x480 OR 8bp, but not both.

48KHz 16bit stereo will fill 2MB quite quickly. (10 2/3sec roughly)

CD quality is good enough. Mini Disc is good also. But I think it may be the audio compression that may also affect quality in some players.

BruceMcF · Post by **BruceMcF** » Sat Jun 05, 2021 6:09 am

32 minutes ago, Travis Bryant moore said:

CD quality is good enough. Mini Disc is good also. But I think it may be the audio compression that may also affect quality in some players.

Except don't forget it's a 6502 hopefully running at 8MHz running the show, so there's not a lot of decompression algorithms that would be able to keep up with the higher quality output levels. If most players are written to support music play in games, those players will focus on generating music that doesn't suck up all the processing time on the music.

To fight against the design of the system in the way you are talking about and using the PCM like a modern audio player involves accepting a drop in audio quality. So when you read the Vera programmers reference guide and see the possible settings of the PCM, like @ZeroByte says, don't automatically assume that each of the settings can be maxxed out at the same time and have something that the 6502 can keep up with.

48KHz/16bit mono might work for a complex waveform that the PSG can't handle and which would be hard to generate by FM synthesis. You find a length where the waveform repeats at 48KHz and repeat the wave, and that has to be a fraction of a second. That works best for percussion, because the length that the waveform cycles for different notes would be different. OTOH, if you are using the PCM to play a sample, you would step down to a lower frequency, lower resolution and likely mono.

From high frequency, high resolution, very short sample length, you could still have a pretty good gated Tom-Tom, since a Tom-Tom only needs to be versions of the sample for three tones, rather than a dozen for a bass or dozens for a piano ... and of course, the gated effect means you can avoid overlapping the Tom-Tom samples. A gated snare would also be possible, where the multiple versions of the wave are the different delays between snare strikes. A gated snare gets to the end of release fairly quickly, so a separate waveform for the attack, decay and hold portions, looping as appropriate, and playing with volume for the attach, decay and release as such, could make for a very nice gated snare.

An issue with both a single channel of FM and with PSG is that there are not a lot of complex harmonics in the tones, so it can sound "tinny", so if you fill in the harmonics with a more complex waveform played on the PCM and have a bass using two FM channels with related but not identical operators settings and tuned a couple of cents from each other, it can make for a much richer sound.

But if you want the villain to tell Mr. Bond that he has fallen into deep kimchi, then it's going to be mono, 8bits, and a much lower frequency.

Travis Bryant moore · Post by **Travis Bryant moore** » Sat Jun 05, 2021 4:26 pm

I think that is why the Amiga or expansion boards exist so you can hand off audio to one chip or expansion video to anther math co processor and so on with the main processors or center processor handles the addressing or routing to the other hand offs like an executive handing off jobs to other workers I suppose. Though I guess no one ever did the 8 bit machines like that.