The Impact of Audio Effects Processing on the Perception of Brightness and Warmth

It is not uncommon to hear musicians and audio engineers speak of warmth and brightness when describing analog technologies such as vintage mixing consoles, multitrack tape machines, and valve compressors. What is perhaps less common, is hearing this term used in association with retro digital technology. A question exists as to how much the low bit rate and low-grade conversion quality contribute to the overall brightness or warmth of a sound when processed with audio effects simulating early sampling technologies. These two dimensions of timbre are notoriously difficult to define and more importantly, measure. We present a subjective user study of brightness and warmth, where a series of audio examples are processed with different audio effects. 26 participants rated the perceived level of brightness and warmth of various instrumental sequences for 5 different audio effects including bit depth reduction, compression and equalisation. Results show that 8 bit reduction tends to increase brightness and decrease warmth whereas 12 bit reduction tends to do the opposite, although this is very much dependent on the instrument. Interestingly, the most significant brightness changes, due to bit reduction, were obtained for bass sounds. For comparison purposes, instrument phrases were also processed with both an analogue compressor and an equalisation plugin to see if any subjective difference was noticed when simulating sonic characteristics that might be associated with warmth. Greater significance was observed when the sound excerpts were processed with the plugins being used to simulate the effects of bit depth reduction.