basic synthesisers are.....basic, with the skills of a three year old you can stick one together, of course you have to find plans for each of the circuit components.  i will not provide extensive circuitry designs.  of course you can find many parts that will fill the bill.  most of this page will be filled with pictures, that is the most effective medium for this type of thing.

flow of sound, the basic components.

what do they do?  simple, the vco is a generator of basic waveforms, a range of frequencies are sounds.  20hz is as low as most people can hear, those are not considered, above 30000hz sounds go so high that only weird people and dogs hear it.  the ease of use of the vco is dependent on your choice of type, linear is the easiest to use simply because it is easiest to interface with a keyboard.

what does it linear mean?  basically it is the range of voltage and frequency change.  there are logarythmic and linear, log. means that the voltage from the keyboard is a direct relation to the frequency output, linear is the voltage disociated from the frequency.


for example, with linear 1volt=1octave, meaning middle c is 1volt different from the next highest and lowest c.  with logarithmic, 1volt=almost an octave, meaning from c to the next it would be 1volt, but to the next it would be 1.3volts, to the next, 1.88volts.  with a keyboard configured for linear, you feed it 10volts you can stuff 10 octaves in it.  with a logarithmic keyboard you feed it 24 to get the same thing.  why is linear preferred?  with it you can use the same resistor value for each key, and the difference between each key voltage is 1/12volt.  with logarithmic you have to have a different voltage for each key, which i assure you is a big deal.

a vco puts out several different wave forms, each basic wave makes a different basic sound, by adding the waves together and changing each one differently you can get very new and wild sounds, also you can replicate real sounds with your own preffered accuracy.

unfortunately the design that i will yak about first will be monophonic, meaning one sound at a time.  i will give basic designs for polyphonic, meaning many sounds at a time, possibly with enough cash all keys at a time could be used simultaneously, each possibly with a different sound.

you could have several vco's, each making a different wave type, this is the way that sounds are made in older soundblaster compatible cards.  each note was made of several sine waves mixed together, this can work for you but is not as fun. a nice little explanation.

the envelope generator is a piece of circuitry that is very nescessary, the waves come out of the vco at full volume all the time, this is not desirable.  but cutting the waves out entirely is not desirable either, so the envelope generator is used to lower the volume of the wave to nothing while allowing it to remain at full strength and stability.  it is set so that when it recieves a voltage it triggers the generator.  if you examine a waveform you will see some characteristics that point out the basic means of sound generation.

when a wave becomes a sound it first rises to a peak, this is called the attack.  the volume drops suddenly, this is called the decay.  then the wave slowly drops, this is called the sustain.  then when the sound ends, it quickly drops to nothing, this is called release.  if you whistle you can hear it, at the start you force the air out of your lips, it rises to a piercing level, then it drops to a comfortable level that you can maintain for a while, then you stop, the sound fading quickly but noticable.  the attack and release are generally very short, the decay is much shorter, the sustain is longer, generally longer than all the others put together.

the next basic component is the vca mixer circuit, the envelope generator needs to have a method of controlling the volume.  the vca and mixer are part of the generator, vca means voltage controlled amplifier.  if you had to control the envelope with a knob you could, but you would get carpal tunnel syndrome from the amount of activity needed to play one song, and instead of three minutes it would take three years.  there is a sister circuit called an envelope follower, you use another instrument to trigger the envelope generator, and the envelope collapses when the other instrument stops.  the envelope generator recieves the signal from the keyboard and starts the envelope, the voltage from it controls the vca.  the problem is that you would have a hard time controlling the generator with the variable voltage from the keyboard, the solution, use a different type of switch in the keyboard.  the type of switch required is a dpst, that is hard to find, use dpdt.  one side of the switch sends the voltage to the vco, one side sends to the envelope generator, the first image shows this in greater detail.

now for example circuits.
envelope generator+vca, it's rather bad but it works.

Hosted by www.Geocities.ws

1