Last year I ported my VIC-20 music player to the creatiVision and implemented the LFSR sound so now I'm fully aware how the SN76489 operates. I don't know if it is the same on a Tandy, but I found that the frequency in channel 2 doesn't at all tune with the LFSR sound (periodic noise) in channel 3 generated from the channel 2 frequency. That is, I only get to use two channels of classic square wave and one channel of narrow bass, with the option to switch to white noise now and then for drum effects.
However as the creatiVision is clocked at 2 MHz, lower than most Z80, TMS9900 and 8088 systems, I seem to be able to get lower frequencies from the square wave channels than those 110 Hz so I don't really need the LFSR. I don't know if this is true for the BBC Micro/Electron too, gotta check that for myself as they're also 2 MHz 6502 systems but perhaps the sound chip can get its clock from various sources so it may differ.
Hi, i was wondering if anyone may have heard of the ALF MC16 from 1978 for the Apple II?
It was the first Personal Computer music expansion and it seems that TI designed the SN76489 based on this card.
The MC16 has 3 square wave sound channels based on the 8253 Timer IC. The Timer offers 3 16 bit timers that were routed through a 8bit (companding) DAC.
As the timer was driven by a 1.782Mhz crystal, very exact tuning was possible.
In 1980 ALF began selling the ALF MC1 that used 3 SN76489 to produce 9 independent sound channels.
The chips were driven by a 2mhz master clock (Q3 from the Apple II bus).
The ALF MC1 was one of the best selling accessories for the Apple II (until 1983) besides the floppy controller. One of the Key-features was the very well designed graphical note entering system. you did not need fundamental computer knowledge to 'program' a song. Interestingly ALF would later make their money with disc copy stations as the song-disks (mostly composed of songs that were sent to ALF by customers) were very well bought and needed to be 'massproduced'.
@carlsson: if you would be interested to port your music player to the Apple II platform, i could provide you with a Apple II computer and a 9 channel sound card (which i have already cloned for myself). As the Apple II has a 1mhz 6502 CPU and a straight forward memory map, it should be easy to tinker with it if you already have some experience with 6502 programming ;-) There are several 100s of songs for the ALF MC1 (and MC16) that used between 3 and 9 voices (available online). The song format is consists of notes and some (not?) processor specific commands (loop-, envelope-, ...-controls).
This thread was very interesting to read so far, pleas give me more
STUFF FOR THE EARS:
Apple II with 2x Mockingboard (=4x 8913) + Midi card recorded directly from a real Apple II:
http://www.applefritter.com/content/ultima-5-fat-tunes
Some 70s and 80s Synthesizer Songs recorded from Tape, LP ... very bad quality...at the time i did not have the recording equipment i used for the Ultima 5 tracks:
http://www.applefritter.com/content/apple-compote-side-b
http://www.applefritter.com/content/apple-compote-music-casette
http://www.applefritter.com/content/test-mp3s-not-finished
http://www.applefritter.com/content/alf-mc1-songs
As you may have realized: Im an Apple II collector ;-) ... but i like all vintage computers the same.
-Jonas