Ring Modulation

Hiro,

 I don't mind you moving my post, I should have started a new thread in the first place. I used to play around with ring modulation for ages, you could get some amazing sounds out of it. Sadly the SID chip only had three voices and you needed two of them to provide the inputs for the ring modulation so you were quite limited in the number of different sounds you could play simultaneously. You currently have 9 channels in Beepcomp plus of course the drums so theres quite a lot of scope to be really creative I guess. I presume CPU is the limiting factor on you being able to generate even more channels?

Hi Hiro,

$100 for a Commodore64 sounds like a bit of a bargain to me. When new in 1980/81 it would have been $650-700 not that I know what the exchange rate was back then - guessing at 1.7 to the pound. It sounded pretty good too because the SID chip actually provided digital control to an analogue core. As my fading memory recollects it supported 4 waveforms, sine, square, saw and white noise and had 3 oscillators, though Commodore called them voices. As I said in earlier post it supported ring modulation by using oscillators 1 and 3 together and it even provided a couple of analogue to digital converters from which you could read the value from a particular pair of memory addresses. With a clock rate of 1Mhz and using Basic you were never going to get a particularly high sample rate but you could read and plot slow changing voltages in the range of 1V, might have been peak to peak but can't fully remember - it was 36 years ago... Quite a revolutionary machine at the time.

It sounds like you have a plan in mind for Implementing ring modulation as a new feature? Seems reasonable having a dedicated oscillator for modulation and using all the waveforms available. Like you said, an interesting challenge!

Hi Neil,

I'm done with my initial quick implementation, and the results I'm getting are pretty interesting, so I invite you (and anyone else who's curious) to test out this prototype version!
sourceforge.net/p/beepcomp/code/ci/master/tree/beepcomp_ringmodtest.exe?format=raw

You can run it by moving the downloaded .exe file into the BeepComp folder inside your Program Files directory and double-clicking it. It might give you a warning, but go ahead and press "Run".

Write for the ring modulator channel starting with @r, and inside the 'R' channel you can use pretty much anything you would use in a normal channel. I haven't done the rewrites for the export function yet, so you won't see any changes in your exported files. But you can test this out in the player for now.

Hopefully this starter example is self-explanatory:


// ring modulation test 1


@G

V1=10
VR=10   // set ring modulator's output level
LOOP=OFF


@1

PRESET=BELL
DECAYTIME=200

L8
RINGMOD=ON // this turns on ring modulation
          // works indepently for each channel
CCCCCCCC

RINGMOD=OFF // this turns off ring modulation
CCCCCCCC


   // @R is used for ring modulator channel

@R
   // default waveform is triangle wave
V10 // you can set output gain here as well
L8
   // let's feed random pitches

O4 E>D<<A>>E<Bb<D>F# // these get fed
O4 G<C>F#<Bb>>A<Eb>C // these get ignored


The modulator channel inherits all the effects available for a regular channel, so you can play around with LFO, ASTRO, Fall and Rise effects... and BEEFUP can come in handy since the modulated signal tends to get its gain lowered:


// ring modulation test 2

@1

V10
PRESET=BELL
DECAYTIME=1200
WAVEFORM=2
BEEFUP=20

O4 L2
RINGMOD=ON
C C C C C C C C
C C C C C C C C
C C C C C C C C
C C C C C C C C

@R

V10
BEEFUP=20

LFO=OFF
L2

ASTRO=6
O1 G > G > G > G > G > G > G > G

ASTRO=OFF
FALLSPEED=3600
FALLWAIT=0
O1 G, > G, > G, > G, > G, > G, > G, > G,

RISERANGE=2400
RISESPEED=3600
O1 *G > *G > *G > *G >
RISERANGE=4800
RISESPEED=4800
*G > *G > *G > *G

LFO=ON LFOWAIT=0 O1
LFORANGE=300  LFOSPEED=4  O1 G
LFORANGE=600  LFOSPEED=4  O2 G
LFORANGE=1200 LFOSPEED=4  O2 G
LFORANGE=2400 LFOSPEED=4  O3 G
LFORANGE=2400 LFOSPEED=8  O3 G
LFORANGE=2400 LFOSPEED=12 O4 G
LFORANGE=3600 LFOSPEED=16 O4 G
LFORANGE=3600 LFOSPEED=24 O5 G


... Let me know what you think!

Hi Neil,

Don't worry, there's no rush! Maybe I was getting something close to the old fashioned alarm clock sound you mentioned, and I was also getting lots of spaceship-like sounds with LFO and pitch bends and these were real fun to play around with I have no idea if these are anything close to what the SID chip produces though...

As I was working on this, the other way of implementing where any existing channel can be fed as the modulator into any other channel is actually a lot simpler than I thought initially. So I want to try this version, too. In this version, you will get a max of 4 independent oscillator pairs working separately so you'll get more flexibility.

You're welcome to email me at beepcomp-at-hiromorozumi.com, or we can also keep our discussion here for any other people interested in this development to join in

Hi Hiro,

I've briefly played around with Ringmod Tests 1 and 2 and that is definitely the sort of effect you used to get with the C64, particularlry the more 'bell' type sound of Ringmod1. The sound produced by your second test is quite amazing. I'd say you've cracked ring modulation, it just needs a bit more time to test it more extensively. I'm going to try and do some some script changes ro modulate against LFO and each of the waveforms that you provide, I'm sure you'll get some very interesting results.

I will take a look at your latest executable and Ringmod3 over the next couple of days. This is really good stuff. One question for you, how would I get LFO frequency to vary slightly, say by +\- 10Hz around a centre frequency of f at a rate of r per second? To make a 'spring' sort of wobble.

Cheers