From gstopp@fibermux.comFri Jun 23 11:07:42 1995 Date: Fri, 23 Jun 95 09:36:13 PST From: gstopp@fibermux.com To: analogue@hyperreal.com, M.J.Smith@acoustics.salford.ac.uk Subject: Re: ring modulators ?? Sure I'll give it a shot... A ring modulator is a device with two signal inputs and one signal output. Technically it is a multiplier - the values of the voltages on the two inputs are multiplied with each other and the result is presented on the output. As you know any analog signal is a voltage over time, so if you call the two inputs A and B the following happens: A = 1 volt, B = 1 volt, output = 1 X 1 = 1 volt A = -1 volt, B = 1 volt, output = -1 X 1 = -1 volt A = -1 volt, B = -1 volt, output = -1 X -1 = 1 volt A = 2 volts, B = -1 volt, output = 2 X -1 = -2 volts etc... Another way of looking at it is as a special kind of VCA - in fact you can use it as a VCA if the device is D.C. coupled (no caps on the inputs). Put a signal in one input and a D.C. envelope on the other input and when the envelope is zero volts the output is zero volts and when the envelope is at max the output is at max. However the difference from a normal VCA is that if your envelope goes negative then you start to get output signal again, except it's an inverted version of the signal input (like if the signal input is a rising sawtooth the output will be a falling sawtooth). This all doesn't sound so special cuz a falling ramp sawtooth sounds exactly like a rising ramp sawtooth to us humans. The trick is that if the two input signals are both in the audio range, then the algebra that takes place has a very drastic effect on the resulting sound. If you multiply two sine waves together with a frequency of X and Y, then you will hear two tones on the output - X+Y and X-Y. X will be totally gone and Y will be totally gone. Things get stranger when the inputs are waveforms other than sine waves, cuz this sum/difference thing applies to each harmonic present. Result? Wierd noises. Space voices, bells, junk like that. Lots of fun. Notice that since a lot of modulars use +/- 5 volt signals, if you multiply them together they will result in 25 volt outputs when the peaks come together, so usually the gain of the guts is less than unity. This scale factor would be A*B/5 for a 5 volt system. A 25 volt signal in yer signal chain may cause some bent needles in your VU meters. Ring modulators are called so because back in the days when there were no chips a ring of four diodes was used for multiplication. Yes I know it sounds easier but actually don't try it cuz it's no good at audio levels. Other names include "balanced modulator" and "four-quadrant multiplier" and "double side-band modulator". A less common animal is a "single side-band modulator", otherwise known as a "frequency shifter", which is made from a bunch of ring modulators plus other strange stuff. These things sound even wierder than ring modulators. As for the subject of D.C. coupling - many times ring modulators will have caps in series with the inputs to block D.C. offsets to avoid yukky effects like audio thumps. The ARP 2600 has a switch for this. Older circuits like the ones that use the 1496 multiplier usually suffer from calibration problems and require frequent trimming. Newer circuits may use parts like the AD 532 which is laser-trimmed (and about $30 bucks a pop) and is really God's gift to ring modulators (no I don't work for Analog Devices). Whoa - sorry bout the windage, slow day at work. ______________________________ Reply Separator _________________________________ Subject: ring modulators ?? Author: M.J.Smith@acoustics.salford.ac.uk at ccrelayout Date: 6/23/95 15:47 could someone explain to me exactly what it is that a ring modulator does ?? i've got an idea that its some kind of amplitude modulation but i'm not sure... thanks m a t t From lhammond@sol.UVic.CAFri Jun 23 11:11:07 1995 Date: Fri, 23 Jun 1995 11:00:09 -0700 (PDT) From: Lorne Hammond To: Eric Moon Cc: M.J.Smith@acoustics.salford.ac.uk, analogue@hyperreal.com Subject: Re: ring modulators ?? No, I thought it was the addition and subtraction of two frequencies. If they are the same inputs (Jimi Hendrix, Lou Reed metal music) you get a cancellation, and an octave above. ex. 440+/-440= 0 & 880 hz. So far so good, perhaps even musical (ha ha). Especially if you are feeding it sine waves with noovertones/harmonics, whatever. The result is a very nice bell like snakey sound. Add echo and enjoy. But most people put an audio into one side, and use an oscillator as the carrier, the other input. A flute would be a great input for one side, and say an oscillator on the other (which you would have to "tune" to the notethe flute is working on. But, as the flute moves away from the frequency the oscillator is at, all hell breaks loose, and I am not exageratting here. I once described it to someone as about as musical as a dragon plunging down an elevator shaft (Dhalgren anyone?). What is happening in terms of addition and subtraction gets very complex as you use inputs thathave lots of overtones, because each of these are added and subtracted as well. So add a fuzz guitar and the most diehard metalhead will wince. How well i remember the live drum solo, through a ring modulator I had on the soundboard that resulted in the closing down of a dance. Favourite ring modulation recordings. Guess how Ozzy got the "I am Iron man" phrase on that balck Sabbath lp. I duplicated with ease using a mike input and a Maestro Ring modulator (a very very earlytom Oberheim product, his logois on the circuitboard inside.) I have seen US funk bands put them on rhodes piano's for a great bite. Butthe best use has been by top notch guitarists: Tony MacPhee of the Groundhogs,whose "Hogwash" LP is *****. Also Jeff Beck, on Blow by Blow, and Hendrix. TheMaestro has threesliders: Mix, pitch of internaloscillator, and volume. The kickerwas this: two foot pedal inputs (special Dearmond dual purpose pedals): each could provide either controlover pitch, or mix. With two you weresetto use it inatasteful controllablemanner. The pedals are vital in my opinion. Tom also sold some as Oberheims in the LA area. Those ones had twoinput jacks. I am looking for: schematics, and a second pedal. About 10 years ago a frustrated guitarist sold one to me for $75."Your the first person who knows what this is....It is unmusical." 95% of the time, that statement is true. Keyboards with ring modulator circuits include the ARp Odyssey, most modulars, and the beloved Korg MS-20. But forusing them live, it is the Maestro/Oberheim w/pedals. Great way to "getyer Tam-tams out" when you feel like Stockhausen. Lorne lhammond@sol.uvic.ca