24 Jul 2013
Earlier today someone asked me to forward them some links I had on speech processors. This reminded me of a VERY effective speech clipper I built many years ago for a 2m AM QRP transmitter. The audio pre-amp had 2 stages of 6dB/octave pre-emphasis followed by very hard clipping and an active low pass filter to keep >2.5kHz audio levels to very low levels. The signal sounded remarkably punchy and allowed this little 100mW AM transmitter to punch well above its weight. It sounded like a rig running several watts. At some point, after we move, I'd like to replicate the design and give it a go again. It was based around the audio stages I used in the Pye PF8 PMR handheld but with value changes to increase the gain and add the second pre-emphasis stage. Double pre-emphasis meant that there was less clipping at lower audio frequencies and more at the higher end. Compressors are meant to be better, but honestly this little circuit took some beating.