Audio Amplifier

Topics: Photoresistor, Dynamic range compression, Ratio Pages: 2 (522 words) Published: April 22, 2013
Project – “Stereo Audio Compressor”

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Audio compressors that use a light source to control a Light Dependent Resistor (LDR) are not new, and indeed there are many classic optical compressor designs. The design goal of the SOC-1.1 was to further enhance the attributes of optical compression to provide the user with alot more functionality as well as improve the compressor response to real world audio signals. We have carefully examined the characteristics of the LDR and developed a truly unique process to control it. This process we call the Differential Drive Side Chain topology (DDSC).

What is an Optical Compressor?
Compressors and limiters are specialized amplifiers used to reduce dynamic range--the span between the softest and loudest sounds. All sound sources have different dynamic ranges or peak-to-average proportions. An alto flute produces a tone with only about a 3dB difference between the peak level and the average level. The human voice (depending on the particular person) has a 10dB dynamic range, while a plucked or percussive instrument may have a 15dB or more difference. Home

A type of audio compressor that uses an electro optical attenuator to control the dynamics of the processed signal. An electro optical attenuator basically consists of a light source whose intensity is proportional to the level of the input signal, and a photoconductive cell (or light dependant resistor, LDR) whose resistance decreases as the light intensity presented to it increases.

The photoconductive cell controls the volume of an amplifier and attenuates the level of the output signal. Thus when a louder signal is applied, the light shines brighter, the photocell's resistance goes down, and the amplifier reduces its gain, producing the effect of audio compression - for each dB that the input signal exceeds the threshold, the output rises by something less than a dB depending upon how the ratio is set and the exact properties of the photo cell...
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