'Set phasors to stun': an algorithm to improve phase coherence on transients in multi-microphone recordings

摘要

Ever since the advent of multi-microphone recording, sound engineers have wrestled with the colouration of sound by phasing issues. For some this was an anathema; for others this colouration was a crucial ingredient of the finished product. Traditionally, delicate microphone placement was essential, with subtle movements and tilts allowing the producer/engineer to determine when a sound was “in phase” based on perception alone. More recently, DAW’s have allowed us to view multiple waveforms and manually nudge them into coherence with visual feedback now supporting the aural, although still a manual process. This paper will present an algorithm that allows automatic correction of phase via a unique Max/MSP patch operating on multiple audio components simultaneously. With a single button push, the producer can now hear a stereo recording with maximum coherence and thus make an artistic judgment as to whether the “ideal” is ideal, or better to pursue naturally occurring phase colouration in preference. In addition, the patch allows zoning in to spatially separated sound sources, eg tuning drum kit overheads to phase lock with the snare drum or hi-hat microphone. Audio examples will be played and the patch demonstrated in action. Limiting factors, contexts and applications will also be discussed.