Audio mastering is the process of preparing audio for playback on a wide range of playback devices. The main changes to a track during mastering are: tonal balancing and level adjustment. The former is primarily done with equalisation while the latter is primarily achieved with
compression. Other effects that can be used during mastering are: enhancers, exciters and stereo expansion.
The steps taken in mastering a number of tracks are:
- timeline all the tracks in the desired order. Leave a 2 second gap between tracks when producing a CD.
- apply noise reduction to eliminate hum and hiss
- normalize the tracks to set the highest peaks in audio volume to a preset level, the overall audio should never exceed 0 dBfs
- equalize audio between two tracks to ensure there are no jumps in bass, treble, midrange, volume or pan
- apply a compressor (for example, 4:1 starting at -6 dB) to compress the peaks but to expand the softer parts
- apply a dynamics compressor to compress only specific frequencies that generate the audio peaks
- in the case of mastering for broadcast, the bandwidth of the signal has to be reduced. For example for TV broadcast: apply a high pass filter at 80 Hz with -18 dB/octave to filter out low frequencies and apply a low pass filter at 12 kHz with -9 db/octave to filter out high frequencies
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