I made a terrible vocoder earlier and got some help on it here:
My new implementation is much better. I'm using the band pass filter described in the document suggested on the old question. It seems to work much better, but the carrier wave is bleeding heavily into the output signal to the point where I can faintly hear some good vocoder sound effects behind the sound of the carrier wave. This bleed gets louder when the input volume is higher. Is this a common and easily fixed problem or should I give more info for you guys to help me debug this?