the oscillator in my 8bit pitch shifter is bleeding thru to the output

[big bustle]

i'm messing around with an 8bit pitch shifter ic and while i really feel like im getting somewhere on it the biggest problem is that the on board oscillator is bleeding thru to the output. i'm hearing a 10.5khz whine on the output.

is there an easy way to some how get rid of this?

[oskar]

What ic is it? One of those toy FX chips?

[big bustle]

yeah. its the ht8950

[oskar]

link to the chip datasheet please!
Are you using a schematic for it? link...
Is the clock generated onboard the chip or is it a stand alone oscillator? edit! onboard it was...

If you're following a schematic from a datasheet remember it doesn't have to be super duper but more intended as a starting point.

[oskar]

The easy way to get rid of it is with a lowpass filter. Start with a simple RC filter at ~4k and see if it suits your needs.

[big bustle]

datasheet:

http://www.alldatasheet.com/datasheet-pdf/pdf/64502/HOLTEK/HT8950.html

i started from the datasheet schem.

if you take a look at the data sheet it has an rc filter.

the problem is i really want to keep the highs int here as much as possible.

but now that i think of it the sample rate is 8k so anything above 4k shouldnt be there anyway

im a little confused about the rc filter stuff. i read a ton of stuff but it hasnt sucken in. i did find some rc calculators.

if you could give me a little nudge in the right direction as far as what i need in the rc that would be super awesome

[oskar]

Well if you have a filter with a cutoff of 4kHz, that is where the signal has been just starting to be affected by the filter. If the filter is only 6dB you will hear signals higher than that for sure.

There is more than one schematic in there. Are you using the 16-pin with LM386?

If you look on other effects using delay chips you'll see that they all use different techniques to deal with the sampling rate, aliasing.
Filter, pre-emphasis and companders ( companders is not for the aliasing problem but to increase dynamics )... The lowest part count solution is probably a "pre emphasis/post deemphasis" filter like the one in the PT-80 (ggg). The first (I think?! ) and last OP in the sound chain. Check it out!

[big bustle]

im using the 18pin chip

im interested in the "pre emphasis/post deemphasis" filter like the one in the PT-80 because you said it was the lowest part count.

im looking at the schem now and im not sure what i should be looking for

what exactly is pre/post emph? is it like dolby?

[big bustle]

i should say that i really like the aliasing.

and here's a link to the pt80 schem

http://www.generalguitargadgets.com/diagrams/pt80schem.pdf

[oskar]

im looking at the schem now and im not sure what i should be looking for

Look at the first half of the TL072. The 1k/10k gives this amp a general amplification of x10 but the 15n cap will block lower frequencies so they will see a higher resistance and thus not become as amplified. Also the 470p feedback cap will cut lows. The OP at the output is set up to deemphasise/ cut the high frequencies...
Then there is a 18dB filter around a transistor after the delay chip and before the expander.
Frankly I'm not sure what filter specialises in what but isn't there a rather long project text around this explaining most of it? I think so...
All that is done is to increase the dynamics of the delay chip and to get rid of whining sounds from the clock...

what exactly is pre/post emph? is it like dolby?

Sort of... but more like what they've done to old records... RIAA...

Dolby is more advanced ( I think   :/  ) with compression involved.