Waveform variations

All sound is made up of a repeating vibration.  This vibration's shape, of course, is known as a waveform. Most electronic music instruments offer some basic waveform shapes, then have filters, distortions, etc to modify the existing waveform.  I wanted to write about another type of waveform modification called chaining or replacement modulation.  A waveform usually refers to a single cycle or period of the repeated pattern. This first figure shows a couple of typical waveforms found in most synthesizers.  The top waveform is usually called a sawtooth wave, and the lower one is usually called a square wave.

Chaining is very similar to replacement modulation, except that chaining occurs when you have complete cycles of waveforms chained together.  Replacement modulation, in contrast, is when you have partial waveforms substituted within a single cycle of a waveform.

Let's consider the length of a waveform.  Normally, we would think about a waveform as a single cycle, but what happens if you consider the repeated pattern to be 2 or more cycles?  Your ear would certainly hear the same sound, but you could say that the fundamental frequency was different, with a different emphasis on the harmonic spectrum.  If the 2 cycle pattern consisted of 2 different waveforms, then you would hear a different tone than the single cycle pattern, one octave lower.

Now, we can take the two different waveforms from the first figure and switch between them either within the same cycle or every other cycle.

On the left we see an example of replacement modulation on top, and chaining on the bottom.  There are not many commercial non-modular synthesizers that do this - Casio CZ and SC Prophet VS come to mind, but typically this has to be patched on a modular synthesizer.  There are several options when it comes to ways to patch this idea.  Most options revolve around a sequential switch or voltage controlled switch or fader module.

Using an analog sequencer to control the switching, one could easily have long chains of different waveforms repeating as one cycle.  The following figure shows 2 cycles:

It is also interesting to use a fader module instead of a switch because you can have varying degrees of mixes between 2 separate waveforms instead of either one or the other.

As a final note, I want to mention that if you create a patch like this where you are switching between 2 waveforms, say a sawtooth and inverted sawtooth, then used a pulse waveform with variable pulse width to control a voltage controlled switch, you can vary the point of switching between the two waveforms within the same cycle.  The following figure illustrates this idea:

Here, the black waveform on top would be the output, the red waveform shows a non-switched saw wave, and the pulse wave at the bottom shows the switching control.  This can be a powerful alternative to the typical PWM (pulse width modulation) that so many synthesizers offer and any 2 waveforms can be used (or even a high pass output and low pass output of a multimode filter).

So you can play a violin sound, piano, or fantasy!

Where do we draw the line between our imagination and the limitation of the equipment, instruments, and our ability to play them? Is it possible to transcend these limitations.

I recently read an article on synthesizers where someone was asked if ANY sound was possible in synthesis.  The reply was yes. I admit - there are times when I come up with a sound that fully beats all expectations that I had in creating that sound.  In other words, it is beyond my imagination or fantasy.  But then again, there are times when hours of fine tuning and adjustment leads to a sound that falls short of everything I had hoped for. 

I approach synthesis in a very practical, logical, and strategic way.  Maybe it is the engineer in me.  I don't subscribe to the point of view that randomly plugging in things and turning knobs will get you this "wacky" sound.  Each and every patch has a purpose and method and objective.  This is not to say that I don't experiment or try new ideas... but the ideas have an objective and purpose. 

Most all of my experiments start with a question: Sometimes my experiments are things like: "What if I made a through-zero oscillator out of these 2 VCO's into a four-quadrant multiplier out of this VCA and VCF, then modulated a 3rd VCO?" or "What if I take the output of this VCF, run it through a Big Muff, then feed it back into the 2nd input of the VCF and control the phase and gain of the feedback loop" or "What if I build a stringed instrument that uses chimes for sympathetic vibration, but the main pickup is closer to the chimes than to the strings?"  Maybe with this kind of logical experimentation, there is not room for a "fantasy" sound.  Maybe the search is on, and I need to determine what I fanasize about. 

My current fantasy, musically, is not a sound, but a keyboard controller...  one that looks like a piano keyboard with maybe a couple octaves of keys that move up and down, but also slightly side to side and forward and backward.  Each key would spring back to a stable central position when not touched.  This keyboard would respond not only to velocity and note on/note off but also wiggle movement side to side, wiggle movement backwards and forwards, aftertouch/pressure, finger surface area, and finger position along the length of the key!  This is very posible with the technology available with modern accelerometers and cap-sensative switching, but is a mechanical engineering nightmare and would require a lot of planning, clever layout, and coding of multiple microprocessors.

The humble Casiotone.  How many of us, as kids of the late 70's or 80's, had these sitting around our bedrooms?  How many of us used them?  How many of us identify them as a "serious" instrument?

My second keyboard that I bought in the 3rd or 4th grade was a Casio MT-32.  I loved it.  (BTW, the photo is of an MT-68 and not a 32).  I loved making up songs using the auto Casio chord and rhythm, along with my first keyboard, a Univox piano, and an upright acoustic piano.  By the time I was in the 6th grade, I had ended up selling both of these keyboards in order to buy my first synthesizer, with some help from my parents and other money that I had saved.  It was a Roland Juno-60.  I would say that the upgrade was a good one and opened me to a world of synthesis, but gone was the autorhythm and chord accompaniment. 

I am currently obsessed with the autorhythm once again.  Yes, one could easily program similar patterns, basslines, chords, rhythms, and arpeggios with other equipment.  But to have it available in one small little plastic box is very convenient.  I am in the process of modifying (NOT circuit bending! - that will have to be another post) the Casios that I have bought over the recent years to accept an external clock and override the internal tempo control.  This is a tedious process without any schematics, but so far, I have managed to modify 3 of them.  I have also modified both my Boss Dr Rhythm 55 and 110 to allow the same external clocking.

The most difficult thing about this is I am finding that everything uses a different denomination as far as master clocks go.  Some want 12 PPQN (pulses per quarter note) where others want 64, 96 or 192 PPQN.  I will just have to make sure that I label these in some fashion so that I don't have to remember every box's clock division ratio - especially if I plan on modifying more machines in the future.  The substitution clock that I use is from a Garfield Mini Doc.  The Mini Doc has several outputs that make it convenient to extract any of these pulse denominations from the main DIN Sync connection.

I got a call the other day from a friend who had an old Korg sampler to which he replaced the floppy drive with some other device that is being made to "update" storage devices to things like SD cards or equivalent. On the phone, he acted like the floppy was the most archaic storage device to trouble with. I politely told him, "At least you don't have to deal with EPROMs".

This is the control panel to a Simmons SDS-1. It is a hexagonal drum pad with these controls on the side. The sound that the pad makes is stored on an EPROM.

This picture is the inside to a Sequential Circuit Drumtraks.  I originally bought this from Claude S. of the band Anything Box around 1993 or so. I bought it with 26 extra EPROM sounds of different percussion, snares, kicks, and toms.  In 1996, I was friends with Alex and Stuart of the band Bassland.  They had access to an Oberheim Prommer, where you could record/sample sound directly into the machine and burn it on an EPROM in the correct format for different drum machines.  I burned another 20 EPROMS or so with various drum loops, typewriter sounds, 909 kick, 909 snare, 909 claps, and a number of synth clicks, noise, and laser sounds.

What is tempo and how does it affect us?  Do we drive faster when we listen to fast music and slower when we listen to slow music?  Do we chew or eat faster when we have a faster song in our head?

The study of biological rhythms and human time perception is very interesting.  When we are children, our perception of time is very long.  An hour seems like an eternity.  As adults, the hours pass with every blink.  Does tempo relate in the same way?  Do children perceive a slowed tempo as arduous time commitment? How do the elderly relate to the same BPM?  Does out preference to music change partially based on this phenomenon?  I know that there are studies of this.  I have a book, "Biological Rhythms in Human and Animal Physiology" by Gay Gaer Luce, that asks and answers some of this, but a thing such as music preference is a very hard thing to define or measure.

We also perceive time differently depending on the time of day, temperature, mood, etc.  I believe that tempo and stylistic preference are very much tied to these things.  I cannot state how many times I have created a song, then listened to it the next day or week or month, and found that I don't like the song at all.... but then, later still, I will go back to that recording and really enjoy it.  What changed?  Certainly not the recording - but my mood.  Not to say that everything is a golden egg - I do have plenty of truly bad ideas as well.

syntheslalom

So I don't really know what this means or what skiing has to do with an Farfisa organ, but I do love random graphics on electronic musical instruments. I am sure that the designer thought that this was somehow relevant.

The syntheslalom knob essentially is a pitch glide.  When a key is pressed, the pitch starts lower than the key that you are pressing, then it glides up to the pitch. the knob is the offset of pitch or how far off the pitch is from the key you press, then the red lever is the time that it takes to catch up to the pitch. Nice effect.  I wish that it there would be an option to start higher in pitch and fall down to the pitch of the key that is pressed.  Many synthesizers have this feature and drum sounds (especially kick drum sounds) really benefit from a momentary fall in pitch at the begining of the sound.

Today is the second day of a new year.  I have a lot of work to do this month.  My album(s), "The Noise is only Temporary" and "Fireworks" are finally done.  I still have some photos to take for the front cover, but I would like to have "The Noise...." done and manufactured and available online as soon as I can - preferably by the end of January.

There are some excerpts from "The Noise...." that can be heard on my soundcloud page.  I have added commentary over these to share some of my thought and process behind the songs.