Why do we need compression? Consider this: You are mixing a rock/pop song with an average dynamic range of 20 dB. Now you wish to insert a fresh recorded vocal. Usually the dynamic range of an uncompressed vocal is around 40 dB. In other words, a vocal performance would go from -30 dBu to +10 dBu. The passages which happen to be +10 dBu and higher will be heard over the mix. However, the passages that are at -30 dBu and below will never be heard over the roar of the rest of the mix. A compressor may be used in this situation to reduce (compress) the dynamic range of the vocal to around 10 dB. The vocal can now be placed at around +5 dBu. At this level, the dynamic range of the vocal is from 0 dBu to +10 dBu. The lower level phrases will now be clearly above the lower level of the mix, and louder phrases can not overpower the mix, allowing for the vocals to ‘sit in the track.’ The same points can be made roughly any instrument in the mix . Each instrument has its position, and a good compressor can assist the professional in the complete blend.