How to get a pure sine wave on Little Phatty???

rmedine · Post by **rmedine** » Fri Jun 12, 2009 11:57 am

Hey everyone, this may be a stupid question but how do you get a pure sine wave on the Little Phatty? I just got one of these to play around with and I can't figure it out for the life of me! The oscillators don't seem to have it. I see the Triangle, Sawtooth and Square waves but no sine wave. SUrely there is a way right?

Thanks for the help.

Ryan

Sir Nose · Post by **Sir Nose** » Fri Jun 12, 2009 2:11 pm

Triangle is the closest the OSC section gets. You can get a sine wave with the filter resonnace turned way up and the KB Amount adjusted appropriately to get it to track to the keyboard.

CTRLSHFT · Post by **CTRLSHFT** » Fri Jun 12, 2009 9:05 pm

Set Osc to TRI.
Set filter pole to 4.
Set filter cutoff to zero (tri loses basically all of it's harmonic content)
Set resonance to zero.
Play a note.

That's pretty much a sine wave, albeit probably not a perfect one, but it's extremely close.

Cranking the res full and bringing down the cutoff filter works too but doesn't track more than a couple octaves accurately.

sergiovalente9 · Post by **sergiovalente9** » Sat Jun 13, 2009 6:13 pm

CTRLSHFT wrote:Set Osc to TRI.
Set filter pole to 4.
Set filter cutoff to zero (tri loses basically all of it's harmonic content)
Set resonance to zero.
Play a note.

That's pretty much a sine wave, albeit probably not a perfect one, but it's extremely close.

Cranking the res full and bringing down the cutoff filter works too but doesn't track more than a couple octaves accurately.

I may be wrong but why not using a square wave and filtering?.

denoiser · Post by **denoiser** » Sat Jun 13, 2009 6:37 pm

sergiovalente9 wrote:I may be wrong but why not using a square wave and filtering?.

No matter what the waveshape is because when filtering with a very low cutoff frequency you're removing all the harmonics and having basically a sine wave.

(Actually, you're lowering the power of the harmonics above the cutoff frequency so there will be very subtle, and even not noticieble, diferences depending on the waveshape.)

CTRLSHFT · Post by **CTRLSHFT** » Sat Jun 13, 2009 9:59 pm

sergiovalente9 wrote: I may be wrong but why not using a square wave and filtering?.

Of all the waveforms available this has the least harmonic content to start with prior to filtering. Since a sine wave has no harmonic content other than it's fundamental, we definitely want to start with the least possible content prior to filtering.