Episode 4 - TB 303

In depth ranting about the Voltage Controlled Oscillator, Voltage Controlled Filter, Slide Circuit, the Accent Sweep Circuit, and Envelope Generator.

Also includes ruminations on why an Analog Synthesizer would sound different from a Digital Synthesizer, and why a TB-3 will lack something that a x0xb0x or a TB-303 has.

Character.

Notes

  • Click-click (light swtich on and off) "Now?" "nope"
  • Welp, haven't got a new light yet, so back to the drawing … board? So lets do some macreme!
  • Still owe you guys a vlog on marketing and a vlog on learning.
    • Well you're gonna have to wait, cause I am learning how to viHart!
  • Today, we're gonna talk about one of the most important synthesizers in the 20th century: the TB-303. In under 4 minutes!
    • That is the thing that is making the rolling squeeling squeltching sound in the back-ground
  • Imma show you some key tracks, link in the doobly doo
    • Special shoutouts
    • Stay up forever records
    • One Bassline
    • Inner City Junkies
    • I know there are some serious acid junkies that are watching, fire your favorite in the comments
  • limited overview, but as we'll see the
    • TB 303s limits give character
  • Birds eye view
    • VCO (draw these! don't write them!)
    • VCF
    • Envelope generator
    • VCA
  • VCO - Schmancy way of saying Analog sound generator thingamagigger
    • Digital to Analog converter, takes the notes from the sequencer and turns it into a voltage
    • Goes through the slide circuit, one of the character builders
    • All that goes through here is just a voltage, but the slide controller can slow down the swich in voltage
    • how much time depends on a capacitor. These things aren't perfect, there's tollerances, badly machined parts, they wear out.
    • So now we have a pitch, which gets fed into a temperature comensation circuit, then fed into the SILLICON CONTROLLED RECTIFIER
    • Lots of super-electronics nerd things here, but 2 fundamental things:
      • Shape of the saw wave output is based on how saturated the transistors are.
      • Again, physical components with differing tollerances
      • (research transistor saturaiton?)
      • Saw itself, as a funciton of how an SCR works, will have a flat top that is related to the pitch
      • What this really means is that the saw wave of a TB-303 is fundamentally different from a normal saw tooth wave.
    • Now we have a saw wave. yay! but the fun don't stop
    • Square wave of TB-303 is not square. This is what most attempts at emulation fail at (horribly)
    • All that happens is that the saw wave goes into the wave-shaper, and then a "square" wave comes out.
    • This was probably done to give the TB-303 another feature, but done cheap as well.
  • VCF - K, we're gonna have to delve into some sound-nerdisms fir a bit. So hold on to your pants.
    • A filter jsut filters out part of hte noise.
    • Just to make things easy, they're named after what they don't filter. So a Low-pass filter, filters the low frequencies
    • Draw graph like this filters out noise, like this.
    • The TB-303 has an aformnetioned low pass filter.
    • The fitler itself was a design by Bob Moog and is called a "Diode Ladder" due to it's schematic and he held the patent.
    • The TB303 used a variation on it, where you could replace the diodes with transistors, thus skirting the patent issue.
    • Lots of little wirdnesses here including some internet dispute on the number of poles. If you're interested, I've set up a suplimental video
    • Poles show you how much slope there is going to be on the fitler, and bump up the resonance
      • The filter poles on this thing are weird. Someone on the internet simulated it with spice, and found it was basically a 4 pole filter.
      • Some other people have commented that their TB-303s have the capacitor on the final pole put in backwards
      • The jury is still out?
      • Ultimately, the filter itself has a unique sound
    • These transistor diagrams here? yea, that's part of hte filter of the TB-303. I love this box.
  • Envelope generator.
    • Envelopes, which i talked about in the compression video, are what give sounds is shape and movement.
    • A percussive sound like a drum …. differnet than a string bass … or even a violin …
    • Envelope doesn't do anything on it's own, it "modulates" the other things, in this case the Filter and the Amplifier
    • Simple AD envelope, attack/decay Decay knob to lengthen the tail
    • There is a special "accent" mode the envelope.
      • due to the design, it doens't quite reset itself, potentially going higher and higher,
      • "like an animal in distress", more minuta about this in the supliment video!
    • So the envelope then modules the filter and the VCA.
    • VCA's are really quite boring, they just take a signal, and amplify that signal acording to some modulating signal. Bam.
    • And allt his comes out as squelchy TB-303 Goodness.
  • Lots of weird design trade-offs, capacitors plugged in backewards, solder slowly corroding. To waht extent does it affect the sound?