what purpose do inverted sawtooths serve?

[djtaifun]

Hi, just wondering about the fact that some synths, including U-He Diva, implement an ascending as well as a descending sawtooth waveform in the oscillator section. Assuming these are not there just to fill some empty space, what purposes can they serve in sound design?

[trance_lucent]

Sawtooth + inverted sawtooth does subtraction. Depending on the phase of both there are various harmonics can be cancelled. This way many synthesizers generate PWM and pulse/square waves.

Two supersaws (one inverted) results in superPWM waveform.

Also there is another trick even if phases of both are locked at the same value.
If you are using layered bass (various basslines which can even play the same partiture, but are placed at different spectral bands) sometimes there are some bass patches use locked sawtooths and sometimes it is better to invert the phase of one bassline to cancel harmonics at the spectral bands intersection. You can do it using postprocessing of course, or just use inverted sawtooth especially if there are anotrher oscillators in the patch which haven't to be inverted.

[faun2500]

Having an reversed sawtooth as an lfo shape is useful for modulation as well.

[Urs]

The Minimoog didn't have pulsewidth modulation. One used to mix an Osc with sawtooth and one with a ramp (inverted sawtooth), then detune a little bit for classical PWM effects.

[Sendy]

You can also use Osc 1 as an extra LFO by transposing everything down a couple of octaves and shifting 2 and 3 up to the top octave. In this case the direction of the ramp could be heard easily.

[djtaifun]

thanks for the replies, very helpful

[clangorous]

Having an reversed sawtooth as an lfo shape is useful for modulation as well.

Had to share...here's a great article that briefly mentions how George Duke used an LFO with inverse saw mapped to the OSC pitch to create a chirping effect.

http://www.keyboardmag.com/article/synt ... uke/152448

The intro to one of George's songs has the effect:

The Minimoog didn't have pulsewidth modulation. One used to mix an Osc with sawtooth and one with a ramp (inverted sawtooth), then detune a little bit for classical PWM effects.

For fans, here is George awesomely jamming on a Minimoog. Looks like there is another Minimoog just hanging out behind Billy Cobham...must be a "spare":



RIP George

[djtaifun]

I know this is an old topic, but in reply to Urs' suggestion of using inverted sawtooths to create pseudo-PWM: I would assume that the inversion is only consistent when the oscillator have a fixed phase reset on every incoming trigger (key hit)? Then, using phase offset of the normal and inverted saw to create an initial timbre with the combined/cancelled harmonics, you could modulate the phase of one/both oscillator to create PWM. This is my initial interpretation of this reply. But then I get the thought that surely the Minimoog (like most analog synths) didn't have osc phase reset (key sync). So it must have been used with free running oscillators? I will be sure to give this another go with both lines of thought. Anyway, thanks to Urs for this gold nugget from the past!

[lectrixboogaloo]

I know this is an old topic, but in reply to Urs' suggestion of using inverted sawtooths to create pseudo-PWM: I would assume that the inversion is only consistent when the oscillator have a fixed phase reset on every incoming trigger (key hit)? Then, using phase offset of the normal and inverted saw to create an initial timbre with the combined/cancelled harmonics, you could modulate the phase of one/both oscillator to create PWM. This is my initial interpretation of this reply. But then I get the thought that surely the Minimoog (like most analog synths) didn't have osc phase reset (key sync). So it must have been used with free running oscillators? I will be sure to give this another go with both lines of thought. Anyway, thanks to Urs for this gold nugget from the past!

You're right, if you wanted to create a perfect PWM it would need to work something like you described. Of course, typically you cannot modulate the phase of the osc or detune in HZ but only pitch. So, you have to use pitch. We know that pitch scales in a non-linear way so the speed of the PWM sound produced changes up and down the keyboard. I guess it's far from perfect, but it's a trick that is there.

Also, the minimoog did not have a dedicated LFO but could utilize an oscillator for that function. In that case, the two different shapes makes perfect sense and were very usful.

[suthnear]

Also, a ramp sounds quite different to a sawtooth when used with a square sub-oscillator. The SH101 saw + square sub-osc sounds quite different to hive's ramp + square sub-osc, for example...