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The natural sounds of life have an extremely wide dynamic range, from the result of a falling leaf to the roar of a jet engine on take off. The human ear has an automatic gain control which enables it to accommodate all of these sounds from the threshold of hearing to close to the threshold of pain, a dynamic range of approximately 120 decibels.
Even the most modern audio equipment is incapable of handling the full range that the ear can cope with. Analogue tape without noise reduction can manage almost 70 decibels dynamic range between its noise floor and the 3% distortion point. 16 bit digital audio equipment can achieve over 90dB. Still almost 30dB less than the ear's range.
Even if a 120dB dynamic range were possible in audio equipment, would it be desirable and useful? A listener in a domestic setting enjoying the exhilarating effects of a 96dB Sound Pressure Level will almost certainly be causing his neighbour a significant amount of annoyance, if not distress! At the other end of the dynamic scale, a typical ambient noise level of at least 40dB SPL precludes the use of very quiet levels in recorded or broadcast sound media.
Almost always, it is necessary to compress the dynamic range of natural sounds to fit them into a window suitable both for the equipment and for comfortable listening.
Although the dynamic range of the programme material must fit into a 30 to 40dB window, there is another factor in the equation noise. All the sounds that we want to listen to, whether natural or electronically processed, are accompanied by a certain amount of unwanted background noise tape hiss, or the rustle of musicians turning the pages of the score in the studio.
Even if, in the final programme, the noise level is below the ambient noise of the listening area, it may still be heard and is therefore undesirable.
The Compressor/Limiter and the Expander are valuable tools for the control of dynamic range and reduction of noise. Compression reduces the dynamic range of any instrument or programme source. Expansion has the effect of subjectively reducing or eliminating background noise.
Compression and expansion have their artistic uses too. The sounds of instruments and voices can be altered. A mix of instruments can be compressed to give a 'tighter' dynamic effect. Or a previously
The DN500 Plus Dual Compressor/Limiter/Expander offers in a compact unit virtually complete control over dynamic range, for corrective and for artistic purposes.
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