An Investigation into Non-Linear Sonic Signatures with a Focus on Dynamic Range Compression and the 1176 Fet Compressor

Dynamic range compression (DRC) is a common process in music production. Traditionally used to control the dynamic range of signals and reduce the risk of overloading recording devices, over time it has developed into a creative colouration effect rather than a preventative measure.

This thesis investigates sonic signatures, distortion, non-linearity and how audio
material is coloured during the music production process. It explores how methodologies used to measure distortion and timbre can be used to define the sonic signature of hardware compressors and other pieces of music production equipment.

A grounded theory and content analysis study was carried out to explore how producers use DRC in their work, how they describe its sound quality, which compressors they frequently use and which audio sources they process with particular types of compressor. The results from this qualitative study reveal that producers use compressors to manipulate the timbre of program material and select specific compressors with particular settings for colouration effects.

Tests were carried out on a number of popular vintage hardware compressors to assess their sonic signature. Firstly, a comparative study was conducted on the Teletronix LA2A, Fairchild 670, Urei 1176 and dbx165A. Secondly a comprehensive in-depth analysis was undertaken of the 1176 to fully catalogue its sonic signature over a range of settings and to compare results from a vintage Urei Blackface 1176 and a modern Universal Audio reissue. Objective analysis was conducted on the
compressors using Total Harmonic Distortion (THD), Intermodulation Distortion (IMD) and tone burst measurements. Complex program material was analysed using spectrum analysis, critical listening and audio feature extraction. It was found the compressors all have subtle nuances to their sonic signature as a result of elements in their design colouring the audio with non-linear artefacts. The 1176
was shown to impart significant amounts of distortion when used in its all-buttons mode and with fast attack and release configurations. This style of processing was
favoured by producers in the qualitative study.