[sdiy] Noise Chip (was: Re: Homemade synth clone)

Tom Wiltshire tom at electricdruid.net
Sat Feb 16 18:20:55 CET 2019


It only covers a fairly limited range, Walter. My NOISE1B datasheet says "24KHz and 56KHz”, so I must have found those figures in the MM5837 datasheet. That’s a shade over an octave, so not much.

If you want variable-rate LFSR noise  then you could either build a hardware LFSR that you can feed a variable clock to, or add an A/D input to something like my NOISE code and use it to control the length of the delay between samples. Like that, you can control the sample rate between 100KHz+ down to zero Hz if you want.

This is 8-bit arcade explosions - that’s how they were done. Example of the sort of sound:

https://www.youtube.com/watch?v=EXzoh6uJO1w

Tom

==================
       Electric Druid
Synth & Stompbox DIY
==================

> On 16 Feb 2019, at 14:31, Walker Shurlds <walkershurlds at gmail.com> wrote:
> 
> Honestly, that “quirk” makes me think supply voltage would be fun to make CV controlled... although I’m sure it’s been done before, but with this chip it sounds easy.
> 
> Best wishes,
> Walker
> On Feb 16, 2019, 08:13 -0600, Tom Wiltshire <tom at electricdruid.net>, wrote:
>> One other quirk of the MM5837 that hasn’t been mentioned yet is that the clock frequency is dependent on the supply voltage.
>> 
>> If you run it on a higher voltage, you get _better_ quality noise (I wouldn’t say “good”) but the loop repeats quicker: “chuffchuffchuff”.
>> If you go for lower voltage, the loop is stretched out, perhaps to something less obvious, but what you get is nothing like white noise any more. Instead you’re into the realm of 8-bit arcade explosions.
>> 
>> There’s a datsheet here, but it’s only a couple of pages. I’m sure I’ve seen a much more complete one (that mentions the clock oscillator/power voltage effect), but I apparently didn’t save a copy offline.
>> 
>> http://synton.nl/wp-content/uploads/2017/04/mm5837.pdf
>> 
>> Tom
>> 
>> ==================
>> Electric Druid
>> Synth & Stompbox DIY
>> ==================
>> 
>>> On 16 Feb 2019, at 08:51, Michael Zacherl <sdiy-mz01 at blauwurf.info> wrote:
>>> 
>>> Ah, I remember Neil Johnson complaining about the Noise Generator in his Jen SX1000.
>>> Must have been the MN5837 IIRC. Neil replaced that.
>>> So, YMMV, as always. ;)
>>> m.
>>> 
>>>> On 16 Feb 2019, at 04:28, Ben Bradley <ben.pi.bradley at gmail.com> wrote:
>>>> 
>>>> "And anything is better than the MN5837."
>>>> 
>>>> Yes, but like many older instruments, sometimes one really wants is
>>>> "that particular cheesy sound." A modern microcontroller can recreate
>>>> the original bitstream and/or make a much longer pseudorandom pattern
>>>> before it repeats (yes, a two-second loop of noise is audible as a
>>>> two-second loop of noise).
>>> 
>>> 
>>> 
>>> --
>>> http://mz.klingt.org
>>> 
>>> 
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