• Registered: 2022-10-19
  • Posts: 7

Topic: MicroBeast (not bee!)

I'm working on an 8-bit kit computer, called MicroBeast, which features a 8Mhz Z80 (and should be good for 10Mhz) and a simple 1-bit sound path. I'm hoping to get some good sounds out of it, but beyond boot-up beeps have struggled a little converting music trackers to run at the right speed.

I've attached a couple of pictures - one of the computer itself, and one of the audio stage. It has a fairly low frequency cutoff in an attempt to reduce noise from fast switching in 1-bit playback routines - PWM switching above about 50Khz should be able to produce fairly reasonable analogue outputs.

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  • Registered: 2022-10-19
  • Posts: 7

Re: MicroBeast (not bee!)

And here's the schematic.

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  • utz
  • utz
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  • Registered: 2015-06-28
  • Posts: 1,022

Re: MicroBeast (not bee!)

Looking great! Is that a VHS case you're using there?

I'm not a hardware guy so my understanding of the audio circuit is minimal, but I'm guessing the filter should give a nice, bassy sound?

Regarding which audio engine to use as a showcase, the best option would be to write a new one, of course big_smile So we could make proper use of those 8 MHz. I would actually be up for coding something, but I'm going to be pretty busy for the next month and a half, so I can't promise any quick results. That said, please post details about how to address the beeper in code, so I can start scheming.

In the meantime, I would recommend to go with one of the Squeeker-type engines. Shiru's Squat (available in his 1tracker) is probably a good starting point. The advantage here is that Squeeker-type engines use only one output command per sound loop, so you don't need to be too concerned about keeping multiple outputs properly aligned. Basically just stuff a bunch of wait states somewhere into the sound loop to adjust for the higher clock speed. Pretty much every newer ZX Spectrum beeper engine has the cycles for the sound loop counted out in the source code, so you just need to find that and multiply by 8/3.5 to get the number of cycles you need for your machine.

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  • Registered: 2022-10-19
  • Posts: 7

Re: MicroBeast (not bee!)

It's a custom case - like the presentation boxes you get whiskey in.

The filter cuts out a lot of high frequency noise, so you get less of the harsh 'square wave' effect, and more of a rounded sound. That sounds amazing, but really it just means it sounds 'more farty'. big_smile

I'm juggling a lot trying to get things ready for the Cambridge Computer Museum's exhibition the first weekend of November, but will try to play with some demos soon. At the same time, I'll be sharing more details of the machine for those that are interested.

I may also have a development machine spare if someone really wants to play around...