The COMPEX is a stereo (2 input x 2 output) Analog Dynamic Harmonics Control unit. COMPEX is a pure analog signal processor which provides adjustment of the audio signal from low quality signal sources. Audio recordings are often purposely mixed to play on low quality audio devices with small speakers or headphones that have a reduced frequency range.These recordings are predetermined for playing at low acoustic levels, therefore they have very limited dynamic range. Secondly the use of low sampling rates in respect to MP3 and other digital audio formats causes considerable losses of harmonic content and delivers degraded reproduction. The COMPEX features an optical audio compressor, with level dependent filters for reduction of unpleasant high frequency distorted signals from bad signal sources and recordings (compressed audio, Mp3, bad CD, laptops etc.). The COMPEX also features a very high quality harmonics expander, which adds harmonic content to the depleted high frequencies on these recordings. The amount of harmonics added or changed is set by an individual potentiometer.