VOGONS

IBM PC Cassette Interface... as a sound card??

Topic actions

First post, by Ozzuneoj

Posted on 
User metadata
Rank l33t
Rank
l33t

Sorry for the bit of hyperbole in the title...

I was just reading about a piece of software called "Will Harvey's Music Construction Set" and I saw that there was a PC version from 1983. I assumed that given it's age the IBM PC version must have simply used the PC speaker for rudimentary music output... then I read this on the wikipedia page for this software:

The IBM PC version allows output audio via the IBM PC Model 5150's cassette port, so 4-voice music can be sent to a stereo system. It also takes advantage of the 3-voice sound chip built into the IBM PCjr and Tandy 1000.

... excuse me... what? Did any other software do this??

I see that this page also mentions some more details:

1984
Music Construction Set, programmed by Will Harvey, came out for the PC in 1984 from Electronic Arts. It had a real staff, with treble and bass clefs, and had a neato "construction set" motif--you could drag'n'drop notes onto the staff before "drag'n'drop" was a common catch phrase. Best of all, not only did it support the native sound chip of the PCjr/Tandy, but it could play four voices through the normal built-in speaker! (Granted, it was difficult to discern between the voices, but it was possible to hear the overall chord you were going for.) You could even print out the staff on your printer, although it was one long staff down the side of the page, and not nicely formatted sheet music. 😀

So, it seems it could also attempt to do four voices straight out of the PC speaker. I would think that if this was possible then other programs and games (and their talented composers) likely did this as well and maybe it isn't that unusual... or maybe it is?

Regardless, I'm more interested in the use of the cassette port for sound. Was it higher fidelity than the PC speaker because it didn't have the same limitations as the PC speaker circuit? Or was it about the same?

What kind of adapter was used to connect an audio device (tape recorder or stereo) to the cassette port? I have found images of the original software and it appears to have come inside a little thin cardboard book-style sleeve, but I haven't seen any images of a cable, adapter or even a box that would hold one.

I just learned about this like 15 minutes ago and it raised so many questions... I figured it had to be asked.

I'm just imagining some kind of driver for popular games of the time (ones that run on an 8088) that would use this same method to play back, for example, the game's Tandy 3-Voice soundtrack in software, outputting it through the cassette port. Perhaps an 8088 can't even handle doing such a thing in realtime while running a game, but I have a 5150 myself and I would love to see it try!

Now for some blitting from the back buffer.

Reply 1 of 4, by wbahnassi

Posted on 
User metadata
Rank Oldbie
Rank
Oldbie

Interesting. I'm guessing the software internally renders the audio and runs it via the output as a mix. It won't be higg-quality of course, plus it could be too heavy a technique to be employed in a fast-paced game.
I'm guessing the cassette to stereo cable is just the same cable used by many home computers back in the mid/late 80's like the VIC, C64, ZX Spectrum and MSX. The main purpose there of course is to store data on cassettes, and the cable typically came with three jacks on one end: input, output, and remote control. IIRC, only a few data recorders back then offered the option to keep hearing the signal from the computer during recording... so probably the software just somehow asked users to connect the cable to speakers instead.

Turbo XT 12MHz, 8-bit VGA, Dual 360K drives
Intel 386 DX-33, TSeng ET3000, SB 1.5, 1x CD
Intel 486 DX2-66, CL5428 VLB, SBPro 2, 2x CD
Intel Pentium 90, Matrox Millenium 2, SB16, 4x CD
HP Z400, Xeon 3.46GHz, YMF-744, Voodoo3, RTX2080Ti

Reply 2 of 4, by kdr

Posted on 
User metadata
Rank Member
Rank
Member

t

Ozzuneoj wrote on 2024-07-04, 06:22:

Regardless, I'm more interested in the use of the cassette port for sound. Was it higher fidelity than the PC speaker because it didn't have the same limitations as the PC speaker circuit? Or was it about the same?

On the original IBM PC, the PC speaker and the cassette port were both driven by the 8253's timer 2 output (typically in square wave mode). So from a sound generation perspective, they're equivalent.

https://www.minuszerodegrees.net/5150/misc/51 … tte_circuit.jpg

Reply 3 of 4, by Ozzuneoj

Posted on 
User metadata
Rank l33t
Rank
l33t
kdr wrote on 2024-07-05, 04:11:
t […]
Show full quote

t

Ozzuneoj wrote on 2024-07-04, 06:22:

Regardless, I'm more interested in the use of the cassette port for sound. Was it higher fidelity than the PC speaker because it didn't have the same limitations as the PC speaker circuit? Or was it about the same?

On the original IBM PC, the PC speaker and the cassette port were both driven by the 8253's timer 2 output (typically in square wave mode). So from a sound generation perspective, they're equivalent.

https://www.minuszerodegrees.net/5150/misc/51 … tte_circuit.jpg

Boy... what isn't available on MinusZeroDegrees? Such a fantastic site. Thanks for digging that up.

So, it seems that there isn't any additional hardware that would make the output from the cassette port any better than the standard internal speaker. Obviously when outputting to a better quality amplifer + speaker the end result could be substantially better depending on the sound being generated (not to mention an external source would have a volume control)... but aside from that there wouldn't be any benefit over using the internal speaker.

To be honest, even if there aren't any huge sound quality gains I would love it if it were possible to select cassette port output versus internal speaker output on a PC 5150. The speaker in mine is so obnoxiously loud that I have some foam wrapped around it just to make it usable without driving everyone in the house crazy. Being able to run some slightly better sounding speakers with a volume control would be really cool.

Now for some blitting from the back buffer.

Reply 4 of 4, by kdr

Posted on 
User metadata
Rank Member
Rank
Member

In fact, given the circuit design, you could make the case that the PC designers looked at their circuit for the cassette interface and thought "why not add an internal speaker to it?" since it only took a couple of extra logic gates and a repurposed line driver IC....

Go to top of page Go to top of page
Back to Sound
Close window
Close window