Have a Synth kit? Try boosting it with some logic to create a simple ring modulator, an addition that will allow you to create complex sounds that in our opinion, sound eerie, wobbly, metallic, droney and totally amazing.

STEPS:

1. If you have a whole synth kit you can add to your ring modulator to create some even crazier noises! Check out our example in the attached files named "ring modulator extended". You can read about it in the attached file "extended explained"

2. Experiment with your basic ring modulator by tuning the oscillators to see and hear the output change as the sound is modulated.

3. If you have a whole synth kit you can add to your ring modulator to create some even crazier noises! Check out our example in the attached files named "ring modulator extended". You can read about it in the attached file "extended explained"

EXPLANATION:

The ring modulator is best known for it’s use creating the terrifying voices of the Cybermen in Dr. Who. The earliest use of a ring modulator in a musical instrument was the melochord, built in 1947. Over the next few years the melochord was used by musicians and electronic music studios in the avant­underground scene of Europe. The public unveiling of this experimental technology was in 1956 with the release of the soundtrack of the major Hollywood film Forbidden Planet. The music, created by famous husband and wife duo Louis and Bebe Barron who pioneered many techniques in electronic music, used home­built ring modulators to create “otherworldly tones” and is credited as the first completely electronic film score.

This is a basic XOR gate ring modulator. Let’s start at the beginning where the power module is and follow through the circuit to see what is happening. Here we have connected a split that is sending power to two different oscillator modules set to square wave mode. explain why? These two modules connect as inputs to either side of an XOR gate module. We’ve also place 2 LED modules, we recommend bargraphs, but any LEDs will work before the XOR inputs so we can visualize the signals. What is the XOR gate doing to these signals? If we look at the truth table for an XOR gate we can see that the output will be true only when one signal is high and the other is low. The XOR receives “a high” value when the voltage from one input is above threshold voltage (about 2.5 volts) , and the other is below the threshold. In this case the input that is “high” sends a signal to the output of the XOR gate and switches the other input off.

Input A Input B Output

low low low

low high high

high low high

high high low Let’s say the XOR is triggered once by the signal from the oscillator on the left input and then again by the oscillator on the right input. We hear this as two sound waves passing one after the other. Now let’s say this is happening really quickly, we now hear the two sound waves passing in sequence, but we also can hear a third ringing sound. Have you ever rung a doorbell several times in a row and noticed that you hear a persistent humming tone along with each new ring? You are actually hearing the product of the frequencies of the sound waves from each time you rung the bell, and this creates an interesting effect called ring modulation. Ring modulation between the two oscillators (these are the frequency inputs we are using, but you could use others), forms additional signals at frequencies that are not just at integer multiples (also known as harmonic frequencies) of either input.1 Below is a graph of 2 waves and the bottom signal represents their product

(find better) maybe this:

1 These new frequencies are the sum and difference frequencies of the original frequencies and at multiples of those sum and difference frequencies, and thus might sound totally different from the original tones. This third frequency is also referred to as sideband frequency or harmonic overtones.

This creates a complex output that literally changes the timbre, i.e. the way we hear, the tone. Ring modulators are quite common in synthesizers. This effect is called ring modulation because the original circuit of diodes used to create the effect was in the shape of a “ring”. You can read more about ring modulation here: http://en.wikipedia.org/wiki/Ring_modulation

Here is a graph showing how the signals interact with each other:

We used other modules in our synth kit to build out this circuit into something really interesting. You can see the circuit we built in the file labeled “ring modulator extended” ­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­

RING MODULATOR EXTENDED

We have placed a few other modules before the speaker change the sound. We also exchanged one of the oscillator inputs to the XOR gate with a random module. The XOR gate from the ring modulator is an input to our micro sequencer, which we set in step mode. As you might have read in your guide, the 4 knobs on your micro sequencer allow you to control the output voltage at each step. The rate at which the micro sequencer is stepping each step is controlled by the rate at which the XOR module is switch to HIGH.

The micro sequencer module is connected to a second oscillator, which sets the pitch at each step. As we explained before, when the XOR module is triggering the micro sequencer at a high rate, the frequencies from each step will overlap and sound like 3 different tones. This second oscillator is followed by a filter module. The filter takes the audio signal and changes certain frequencies to make them sound louder or “brighter”, this is again affecting the timbre of the sound.

The envelope module’s input is connected to the trigger out of the micro sequencer module. The envelope allows you to control how long it takes for the sound to reach the loudest peak, also called the “attack”, and how long it takes for the speed to reach silence, also called the “decay”. This results in a manipulation of the “smoothness” of the sound. The output of the envelope is connected (via a wire module) to the frequency in on the filter module. Let’s look at the filter again, it is processing the pitch generated by the second oscillator. The rate of this signal processing can be set by an input to the the frequency in on the module. In our circuit this rate set by the signal from the envelope module. This is automating the filtering process. You can also set the rate manually by adjusting the knobs on the filter, but you probably won’t be able to turn them as quickly as the envelope module sends a signal. From here we attach a split module to the output of the filter and connect the signal on one side to a delay module. The delay module is then connected to one channel in a mixer module. The other end from the split passing is connected directly into the other channel of the mixer module. The mixer module allows you to control the level of these two inputs that are feeding into the speaker module. And finally, the speaker module takes this processed, modulated, and mixed signal and makes it audible!

Tip: If you have any bargraph modules, try placing them between different steps to better visualize what’s going on!

Step 2. Experiment with your ring modulator! Try bringing the random to “noise” mode, what kind of sounds are you getting? Turn the first oscillator (input to the XOR) up and down. Notice any difference in the range of the sounds? Now try adjusting the second oscillator (after the micro sequencer). When you put the random module in “noise” mode, the rate of the micro sequencer is now influenced by “white noise” which is so fast that we hear the sound coming through as static, or in this case it sounds a bit like thunder.

Step 3. Remember how one channel of your mixer is just a delayed version of the other? This means that one channel is what is coming out “live” from your micro sequencer, and the other is repeating the live channel, but is always a bit behind. You can use this to create a cool reverb effect. Reverb is defined as “the persistence of sound in a particular space after the original sound is produced”.

Step 4. Try adding a keyboard to the mix! Connect the input on your keyboard to one output of the split module that is connected to power and the output of the keyboard to the oscillator that is connected to your XOR gate module (see diagram in file “ringmodulator2.pdf”).

Turn the oscillator down and play the keyboard. You should find that the keys are influencing the speed of the tune passing through the sequencer. The lower note keys (those near the left side of the keyboard) and slowing it down, while the higher note keys (those on the right) are speeding it up. Why is this happening? When the oscillator is tuned to a frequency below 20 Hz it becomes a low frequency oscillator. The oscillator is operating at a frequency that is lower than that of an audio signal, but it is still modulating the signal by altering the cycle, i.e. oscillation, of the wave. The keys on the keyboard are still offsetting­ or changing the frequency that is input to the oscillator, but in this case the lower notes generate a slower cycle, while the higher notes generate a faster cycle. Try adjusting the oscillator and filter to generate a “whomp, whomp, whomp” sound.

That was cool. Now try turning the oscillator up higher and play the notes again. Now the oscillator is operating at a higher frequency which audio signals can pass through and the keys are coming through as audible notes, so you can play a live melody over your modulated background signal.

VIDEO TEXT

● This ring modulation circuit uses an XOR to mix and multiply frequencies, producing sounds that are eerie, wobbly, and metallic. ● The split sends power to two oscillator modules that are set to square wave mode. ● The two oscillators send signals to the two inputs on the XOR module. ● The XOR module only outputs a "high" signal when one OR the other of its inputs BUT NOT BOTH receives an "high" signal. ● Due to varying frequencies, the two oscillators send pulses to the XOR at different rates. ● Because the two square waves have different lengths, they trigger the XOR to output a "high" signal when they are opposite. In turn, the output is "low" when the waves overlap. ● What we hear is a square wave at the sum of the two frequencies, and a square wave at the difference of the two frequencies.

● This sound output by the xor is the sum and difference of the frequencies output by the two oscillators