PWM on an Apple II

category: offtopic [glöplog]
Enjoy the powers of pulse width modulation on an Apple II!


You can grab the disk image here:

added on the 2011-12-06 06:09:03 by Gortu Gortu
Awesome! That's a track that deserves a demo just as sweet. Very nice frequency range, which is something my poor bleeding ears only too often beg for in 8bit compositions (and I love 8bit and chiptunes in general, handled well).

Do you know if anyone has hacked at the Ensoniqs in IIGSes before as well?

(Yes, I ought to get my butt over to Kansasfest someday)
added on the 2011-12-06 16:30:15 by metoikos metoikos
I think this has been filtered. And why is it stereo anyways?
added on the 2011-12-07 03:30:56 by Exin Exin
Cool stuff now i want an Apple II even more :p
I think this has been filtered.
That's probably from the components in the computer. There might be a simple RC filter (1 pole low pass filter with light rolloff) with the intention of making the sound less harsh. But if you're switching the voltage level on and off with the CPU with a carrier frequency of something like a few 100 kHz, the carrier frequency is going to be almost completely filtered out. Also, there's filtering in the sound device recording it out of necessity. If you're recording at 44.1 kHz, you need a low pass filter at the Nyquist frequency, i.e. realistically a little bit under 22 kHz, to avoiding aliasing the ADC stage.

tl;dr: Filtering happens naturally.

This is not perfect because none of this was designed specifically to get rid of this source of noise, but it does work in some fashion. Which is why it's so noisy.
added on the 2011-12-07 15:20:43 by nitro2k01 nitro2k01
re stereo, I know there's a stereo-enabling card for the IIGS, perhaps there is one for the II?
added on the 2011-12-07 16:05:15 by metoikos metoikos
The demo tune is multitracked and uses both DMS Drummer and DMS Synthesizer. The PWM carrier frequency of both programs is 22kHz.

Any stereo cards for the II also include additional sound generators -- usually in the form of AY chips as in the Mockingboard. The DMS programs use only the standard speaker interface.

The thing about stereo cards in the IIgs is that the ensoniq chip does natively support multiple channels, yet the motherboard does not utilize them without additional circuitry.
added on the 2011-12-07 17:47:54 by krue krue
Nitro: So what is this about? I had an Apple 2 and trust me, samples are something thats almost impossible on that machine. Especially if they are mixed or in some kind of tracked format. since you have neither a timer nor any kind of interrupt. So you can simply forget about a "few 100Khz". (If you have a Zipspeed, maybe 100.)

A 1Mhz 6502 may put a sample through at something round 20Khz. And then its just load, shift, store, inc address until someone presses a key.
And the memory in a Apple 2 (originally 4K) is 48K or 64K(what i had) at best with around 1MB with bankswitching. (Thats the biggest expansion i've seen so far)

Also WTH is this with this stereo anyways. The Apple 2 has a BEEPER.

With the mentioned mockingboard its a while different story. Its 2 VIA's (6522) provide timers and the AY's have 4 bit volume registers each.

I always wanted to build a mockingboard myself. I have the VIA's and the AY's.....but software is rare. But the board looks simple and a few ripoffs have been made with smaller board layout.
added on the 2011-12-08 02:37:15 by Exin Exin
Maybe he has a Mockingboard.

Or, and this is probably crazytalk, maybe he created the track with samples on another machine, and found a way, probably a tool, to convert it to a hard-coded form that would talk directly to the squeaker and found some other hackalicious software which I can't imagine way around the lack of hardware timing?

Damn, I wanna know . . .
added on the 2011-12-08 13:40:28 by metoikos metoikos
Afaik, all of the output was generated using both the drummer and synth, and was mixed on a PC.

Maybe use two Apple II's? :-)
added on the 2011-12-21 04:43:30 by Gortu Gortu
They just released another Apple II demo over at this years Kansasfest https://8bitweapon.bandcamp.com/album/class-apples with Classical music done on the Apple II and IIGS hardware
Talk with some oldschool Apple II demosceners: https://archive.org/details/2017_Kfest_Brutal_Deluxe_Keynote

Recorded by Jason Scott
You know, just because there's Apple II in the topic title doesn't mean that you need to dump any Apple-related links into the topic.