Reverb/Delay + Ring Mod help

[GammaFlex]

So I'm working on a reverb/delay thingy, similar to the Ersatz Verben by Culturejam but with some different stuff.

I am looking for a simple ring mod to use as a part of the delay mix. Do you guys have any suggestions?

I know some ring mods can be quite harsh, but perhaps if there's one that's a little smoother it might work better with delay?

[blackieNYC]

why not introduce an audible-range LFO into pin 6 of the pt2399?  this LFO from Merlin https://dl.dropboxusercontent.com/u/57831278/JennyGreenteethBuildDoc.pdf will go up to 50 Hz or so, and at a large depth of modulation that's a great "pseudo" ring modulator.  back off on the LFO depth for a mix control of the ring.  Of course you are modulating your delay time, but if you kick in the ring modulator you will still sound echoey at the same time.  If I was to do mine all over again I would suggest messing with it and getting an even higher freq out of the LFO.  If you had up to 200 Hz or higher it would be a great range of sounds.
If you want it completely separate there are gazillions of ring modulators.  being lazy, i went for the very simple beavis 567 tone decoder circuit.  I have a cmos version of the 567 coming, which will supposedly get rid of the oscillator bleed thru.  But the above LFO circuit is a better way to modulate than a 555 timer or any square wave clock.  They take a little effort in getting rid of ticking or oscillation bleed thru. folks have done it though.
Oh yes - another thing about the Jenny Greenteeth and many modulating pt2399 circuits - you have to sever the dry blend to get the best ring mod sounds.  Almost all of them have a max blend of 50% wet 50% dry. I have a 3pole switch for the RM that changes a speed cap in the LFO ( to give me lower speeds, optional), cuts the dry signal, and removes an attenuator on the delay line so your output volume is high enough when you kill the dry.  And I managed to drive an LED also.  Nice to know if your ring modulator is on or off.  I'm not posting my schematic because I wouldn't do it the same way again, and some changes should be made to it.  But I do recommend the general technique.

[samhay]

If you modulate pin6 with an LFO and lift the dry signal you will get pitch modulation, but unless you have feedback, then you won't get any echo - this is how the 'Cherub' chorus works. If you make the depth pot too large then it gets really weird and I suppose an A10k pot in series with the modulation could give quite interesting pseudo-reverb sounds.
http://www.diystompboxes.com/smfforum/index.php?topic=106854.msg968863;topicseen

[Digital Larry]

While I can't attest to the possibility of getting ring mod sounds by audio-frequency modulation of delay time, in my digital experiments I have reduced ring modulator harshness greatly by low passing the audio prior to ring modulation.  And I mean pretty severely, e.g. to 500-1000 Hz.

[ElectricDruid]

While I can't attest to the possibility of getting ring mod sounds by audio-frequency modulation of delay time, in my digital experiments I have reduced ring modulator harshness greatly by low passing the audio prior to ring modulation.  And I mean pretty severely, e.g. to 500-1000 Hz.

..which might suggest that audio-freq mod of a delay line would make for a nice sounding ring mod effect, since delay lines usually have LP filters both before and after them, which has got to help roll-off some of that ring-mod metallic clang.

Since what you're doing with the mod of the delay line is pretty much FM, the shape of the modulating waveform will make a big difference too. Anything with a lot of high frequency content (ramps or squares) will make for a much harsher, more brittle sound than smoother, less harmonic waveforms (sine or triangle). So think about the oscillator you use for the modulation too.

HTH,
Tom

[Digital Larry]

Sorry if I sound skeptical, but what makes you think that delay line sample rate modulation causes "ring modulation"?  I can imagine that at some sweep extremes you are getting some aliasing because the sample rate is too low.  Help an old *&^% understand. 

[blackieNYC]

I'm sorry I can't find a clip, but pitch it even amplitude modulation with an LFO is the audible range is often referred to as pseudo ring modulation.  Perhaps aliasing is a better description of the effect, but it really does sound like ring modulation. A bit more manageable even.  
This may be a ring mod in the true sense, but in any case it's an audio freq modulated by another, no? Can someone chime in between the difference between the pseudo RM and the real thing? http://experimentalistsanonymous.com/diy/Schematics/Ring%20Modulators%20and%20Frequency%20Shifters/Old-style%20ring%20mod.gif
Not sample rate modulation- delay time modulation.  Like turning the delay time pot up and down at a certain rate.  When that rate becomes an audio frequency, the magic happens.  Agreed- if your delay is long this will be odd.  Good point.  Getting RM out of a delay limits the functions of the pedal somewhat. 

[ElectricDruid]

I'm sorry I can't find a clip, but pitch it even amplitude modulation with an LFO is the audible range is often referred to as pseudo ring modulation.  Perhaps aliasing is a better description of the effect, but it really does sound like ring modulation. A bit more manageable even.  
This may be a ring mod in the true sense, but in any case it's an audio freq modulated by another, no? Can someone chime in between the difference between the pseudo RM and the real thing? http://experimentalistsanonymous.com/diy/Schematics/Ring%20Modulators%20and%20Frequency%20Shifters/Old-style%20ring%20mod.gif
Not sample rate modulation- delay time modulation.  Like turning the delay time pot up and down at a certain rate.  When that rate becomes an audio frequency, the magic happens.  Agreed- if your delay is long this will be odd.  Good point.  Getting RM out of a delay limits the functions of the pedal somewhat.  

There are three, or depending on how you see it four, different things you can do:

1) 2 quadrant amplitude modulation - basic AM. This is where you control the level of one signal with the level of the other. Modulates a bipolar signal with a unipolar one.
2) 4 quadrant amplitude modulation - genuine "ring modulation". This is where you control both the level and polarity of one signal with the level and polarity of the other. Modulates a bipolar signal with another bipolar one.
3) Frequency modulation - Another kettle of fish.
4) Phase modulation - amounts to the same thing as the above.

What the delay time modulation is doing is basically introducing a variable phase shift, so I'd say it's an example of (4), which is to say, it's a frequency modulation. Since the BBD is a sampled system, it is also an example of a sample rate modulation, and aliasing is definitely going to be an issue to consider. The best remedy for that is to keep the clock frequency high (e.g. delay time short, or high rates with long delay lines).
In practical terms, they do all sound much the same - I'd describe them as different flavours of the same basic concept. AM is milder, Ring mod is wilder, FM can get really discordant if you're not careful.

HTH,
Tom

[GammaFlex]

This is some really good info.

I suppose that with a simple ring mod like Tim Escobedo's "thing" modulator would be an interesting effect if blended together. What I'd like to try to do is be able to tune (right word?) the ring mod to add a sort of resonance to the overall effect. What would be the most efficient way to accomplish this with a simple ring mod? I'm a newb when it comes to things like ring mods, I've only ever built fuzzes/boosts/distortions and other more simple things but I'm looking to expand my hobby a bit.

[Eddododo]

look up ray rings ring modulator on circuitsalad.com

[Digital Larry]

This is some really good info.

I suppose that with a simple ring mod like Tim Escobedo's "thing" modulator would be an interesting effect if blended together. What I'd like to try to do is be able to tune (right word?) the ring mod to add a sort of resonance to the overall effect. What would be the most efficient way to accomplish this with a simple ring mod? 

At the risk of engaging in self-promotion and going off topic in the non DSP section, I have created some pretty crazy things in DSP using the Spin FV-1 chip and the SpinCAD Designer software I've been working on for the last year or so.  The craziest one was a stereo envelope controlled ring modulator that sounded a bit like someone doing overtone singing while bungee jumping.  Bit I'm not certain that FV-1 projects are good for beginners as SMT and programming the thing from your PC are involved.  To do the same thing in analog would require a lot of work and tweaking.  It is also possible to add resonant filters to your patch that track a knob, follow the signal envelope, or an LFO for example.

[blackieNYC]

I stand corrected- sample rate modulation IS delay modulation. Thanks digital larry, for visiting the shallow end of the forum. Don't mind the warm spots...
Somebody's helpful white paper:
https://ccrma.stanford.edu/~dattorro/EffectDesignPart2.pdf

[Digital Larry]

Hey blackieNYC, no problem, even stuffed hat types like me learn new things from time to time here.  For example, I now believe that  frequency modulation,  which happens when you do sample rate/delay time modulation, could generate audio artifacts which sound something like ring modulation.  The main factor being that they create new information (sidebands) which is not harmonically related to the input signal.  Sometimes I have a hard time understanding concepts which do not fit neatly into (or at least were not explained using terms of) my mostly-mathematically based understanding of electronics and signals.

For example, let's start with tremolo (slow amplitude modulation).  Kinda sounds a lot like two guitar strings very closely tuned "beating" against each other.  But that's two signals at actually different frequencies mixing together in the air.  Which kinda sounds like a chorus, which is a slow periodic up and down frequency modulation of a signal mixed in with the original.  So the idea of increasing the modulation rate into the audio range opened up new possibilities which I hadn't considered before.

What I wonder beyond that is whether audio-rate sample rate/delay time modulation gives the same end result as digital chorusing with an audio rate LFO.  At least in the FV-1, delay time modulation is created by skipping samples (changing the point in the delay buffer that you read back, but at a fixed sample rate) rather than adjusting the sampling rate of a fixed length delay line, such as any BBD or the PT2399.  I lack the mathematical understanding of what happens with sample-skipping to form an intuitive guess.

[PRR]

D.Larry-  Do you own a grader or is that just art?

[Digital Larry]

Hey Paul, it is not mine.  That is the Holy City property which is across the street from where I live.

[merlinb]

Sorry if I sound skeptical, but what makes you think that delay line sample rate modulation causes "ring modulation"? 

Quick sound clip of Jenny Greenteeth:
http://dl.dropbox.com/u/57831278/JennyGreenTeeth.mp3

[Digital Larry]

Thanks for taking the time to make a demo!  I'd put that into its own category of weirdness.  Seems a little thinner/cleaner than ring-mod.  Buddenyway.