Thanks. Attachment added. I'm traveling now so will take time to respond. But once I'm back at the physical Lisa, I will try to update this thread if/when I discover more.
1 2022-04-14 09:37:19
Re: Video about 1-bit sound in Apple Lisa (12 replies, posted in Other Platforms)
2 2022-04-13 18:10:08
Re: Video about 1-bit sound in Apple Lisa (12 replies, posted in Other Platforms)
I don't think there are 9 pulses; the vertical spacing looks arbitrary to me and does not really correspond to volume changes, something else must be causing the spacing (and quite possibly my cheap oscilloscope). There are clearly 8 levels heard from the speaker, and the code responsible for the above is attached.
Yeah, I don't expect people to drop everything and start working on the Lisa... it's been waiting 40 years, can wait a few more! I'll try to experiment myself a bit within limited capabilities. I'll be refreshing the thread with progress.
Ray Arachelian is working on fixing the emulator; he acknowledged my yesterday's feedback.
Lastly, just a minute ago I tried a crazy idea to simply keep shoving new and new series of 8 bits to the shift register without waiting for the sound to finish like below, and it's working — you can basically keep flooding the shift register without changing its state first in any way. Like this:
MOVE.W #$20,D6
loader MOVE.W #$FF,D5 ; load only 1s first, then change pattern with every iteration
pusher MOVE.B D5,SHR1(A0)
MOVE.W #$00D0,D4 ;set some arbitrary delay constant
ticker DBF D4,ticker
DBF D5,pusher
DBF D6,loaderIt didn't choke or anything. Produced weird whizzing sound because we iterated through all possible 8-bit pulse train shapes.
3 2022-04-13 14:01:47
Re: Video about 1-bit sound in Apple Lisa (12 replies, posted in Other Platforms)
utz wrote:
(...) However, from the video it sounds like the upper end is somewhat compressed, ie. the increase in volume is not linear. Could you check that with your oscilloscope?
The increase in voltage looks linear (see attachment), but linear voltage increase does not translate to linear power increase, so probably that's why we hear relatively strong difference between quiet levels, and relatively negligible at the loudest levels.
That's for frequency 440Hz, 50-percent duty cycle, notes at individual volume levels played in quick succession.
Also, I am traveling for the next 10 days so won't be able to test anything on the Lisa. But I'll test when I'm back if needed.
4 2022-04-12 20:26:25
Re: Video about 1-bit sound in Apple Lisa (12 replies, posted in Other Platforms)
Thank you for watching utz and for the kind words. And I'm sorry for totally missing the fact that you worked on the PET implementation with Shiru, I didn't realize that, I would've mentioned!
In any case yes, the volume gain definitely doesn't sound linear, and I'll do the measurements shortly and post here, good idea.
Also, Ray Arachelian is actively working on fixing the LisaEm based on my feedback, so hopefully soon it will be easier to compose stuff; see here for details https://lisalist2.com/index.php/topic,255.0.html
5 2022-04-12 08:35:48
Re: Video about 1-bit sound in Apple Lisa (12 replies, posted in Other Platforms)
Great. I'm really hoping you can exercise the techniques you used on PET, but on the Lisa... very interesting is the 3-bit volume control available on low level which is not available on other platforms of that era (from what I was able to research). In my experiments I was able to switch very fast between lowest and highest volume which created interesting echo effects.
Also funny how I found your article on the PET very shortly before publishing my video, glad I did because I was able to reference it!
Apple Lisa has a strong cult following but (almost) no demos, so there's a fertile ground and large audience if you ever find time to work in it.
6 2022-04-12 07:09:28
Topic: Video about 1-bit sound in Apple Lisa (12 replies, posted in Other Platforms)
Apple Lisa has a 1-bit sound output. I'm exploring the possibilities in this video + challenging others to try and code an engine for that platform for which I lack skills. I know that Shiru (whom I've given credit in the video) has done a lot of work on shift register on the PET platform; Lisa offers a similar approach but with a 68K procesor + software-controlled volume.
Lisa hardware is relatively rare, but there is a good emulator https://lisaem.sunder.net; problem is that it does not support sound correctly yet, but its author is actively working to fix it. Once fixed, I hope skilled people will start coding a lot more for that platform, and explore its sound peculiarities.
For now I had to test all the experiments on a physical machine. I hope with this post to excite others about this platform for which (from what I know) the demoscene is almost non-existent. Except for one Requiem demo which, however, has very simple sound only.
The video is here: https://youtu.be/zKRgtbadZ_U
There's also an accompanying article here: http://forgottencomputer.com/retro/sound/#applelisa