Triangle and Gate

Having demonstrated the ramp and square waves were working well, the latter with PWM I went on to make the triangle waveshaper. This is shown in this section of the PicSynth Schematic:

This involves feeding the non-inverting input with 1/2 VCC. In my case since I'm still running of 5V from the Arduino it's 2.5V.  When I first tried it I was at my initial note - A (440HZ). I got a reasonable looking triangle:

However I found as I lowered the pitch it looked less like a triangle a more like a sort of rounded off square wave:

Interesting enough it still sounds reasonably different to the square wave, quite a bit smoother with less buzz. I experimented with some different values for the integration capacitor and decided that 4.7nF seemed to give a better overall frequency response - still giving an OK triangle at lower frequencies and not attenuating the higher frequencies too much. 

At the same time I did some experiments with a basic gate. Eventually I'll be able to gate the envelope generator but for testing purposes it would be useful to turn the sound on and off in response to notes rather than simply adjusting the pitch of a constantly running oscillator. I experimented with trying to turn the timers off between notes but this caused annoying effects at the start of each note.  Finally I just simply added an NPN transistor with the base attached to an Arduino pin via a 1k resistor to the ground connection of the output that leads to the amp. This is a bit noisy when the gate is off but it's kind of enough to give the idea of what "real" notes would sound like.