Hacker News Reader

Comment by feintruled | Hacker News Reader

The article ends to a link to a video that shows off the technique and it blows my mind the Spectrum beeper could produce this: https://www.youtube.com/watch?v=7cOu32m3wvQ

View on HN

Turns out that it's actually 2-bit and not 1-bit. It uses a combination of the EAR and MIC jacks, and when you output through the MIC jack, it slightly boosts the EAR jack. That gives you 4 possible levels, but they are not evenly balanced.

No, it is not a 2-bit. It's an honest 1-bit, no any hardware tricks, only ONs and OFFs.

Yes, both Beeper and Recorder bits are changing, but both to the same value, along with all other bits of port FE due to optimization (instruction CPL to set beeper bit to 1 instead of LD A, 16).

I gotta try this on real hardware, reading the original article it seems it's barely audible without an amplifier, unlike on an emulator.

Will post an update after I get back to my parent's home, where I have these beauties that launched me into computer science: https://imgur.com/a/GKrA0vX

I created a program like that back in the day. In my case, I recorded my voice through the "MIC" input and played it back through the TV. A few seconds of sampled audio required the entire available memory. While I fully understood what was going on, I thought it was magical that the Spectrum could "speak with my voice".

On ZX-Spectrum? There was no "MIC" input on ZX-Spectrum, not that I know of. I was in high school at the time with only a rough understanding of the hardware but it was kinda obvious to me that whatever I plugged into the casette input port was only read as "0" or "1" by the IN <port> (forgot which) instruction. So not really possible to record voice at the time (didn't even know of PCM anyway), but I tried to decode Morse transmissions from radio. Never got anywhere with the software but my ear got good enough at some point that I could decode them myself by hearing :)

With proper volume control, even one bit could probably sound voice-like enough to a person in the 1980s.

It may be feasible to retrieve a pcm for a very short clip by playing the same recording at different levels which then could be converted on the same machine to a sequence of opcodes playing a more realistic voice.

On the Speccy at the time we had no volume control, only frequency... or more accurately you could but the frequency and the volume were tied somehow: https://retrocomputing.stackexchange.com/questions/14655

You would adjust the volume on your tape player to do what I proposed.

There was Z80 code to record from the MIC socket in one of the small books (Melbourne House maybe?) that came out in the early 1980s. I remember borrowing it from the library and it worked! Heavily quantized of course by the snapping to 2 or 0.

Also some games had sound samples, Activision’s Ghostbusters had a couple.

Nope. I did the same thing myself with my Spectrum. I guess I was 14. I didn't have a microphone so I tried it with my dad's stereo headphones. I got the idea to try it after looking at the Z80 machine code of cassette saving and loading routines. Maybe it was also after ETX came out, first game I remember with speech samples. (Terrible game). I forget the details now but it's all about the timing between turning the mic/speaker on or off.

> There was no "MIC" input on ZX-Spectrum, not that I know of.

Don't be daft. Of course there was. It could save programs onto cassette as well as load them from cassette.

The ports are labelled MIC and EAR because that's what you connected them to on the cassette recorder.

More mind blowing, that entry took _second_ place! First place would probably break my brain for the day so I won't look it up.

Release party: DiHalt 2026 summer Compo: Demo Platform: zx spectrum Ranked: 2nd

Sounds pretty good. Reminds me of the Demo Scene and the types of music they were able to create.

Reply on news.ycombinator.com