Timbral Characteristics of Off-Axis Microphone Response
Start date: 2019
End date: 2022
This research project is investigating the properties of microphones that can lead to them each imparting a characteristic tonal quality or timbre to captured sounds. A particular focus is the off-axis response, i.e. the behaviour of the microphone when the sound source is not located directly in front of it.
A literature-based investigation has been undertaken to determine how a microphone's design parameters are likely to influence measurable characteristics such as frequency response, transient response and distortion level, and how these measurable characteristics are likely to vary with source-to-microphone incident angle. Relevant design parameters have been found to include microphone body shape and dimensions, backplate type (for a condenser microphone) and damping, and acoustic phase-shift network type and length (for single-diaphragm directional microphones).
Hypotheses based on the findings of the literature-based investigation are now being experimentally tested using controlled acoustic measurement, and listener assessment, of a selection of microphones and sound sources. Testing is being conducted with an angular resolution of 5° at source-to-microphone distances of 0.5 m, 1.25 m and 5 m.
A combination of literature-based research and experiments using human listeners will establish the impact of all of the above on the perceived timbre of sound captured by a microphone, and will determine the timbral characteristics that are most affected.
The intention is then to develop computer models of timbral perception that will allow automated prediction of the on- and off-axis timbral characteristics of microphones. Such models have applications in microphone design, development, marketing, selection and use, e.g. at the design stage, software could predict the timbral effects of alternative head-basket shapes under consideration; for the end-user, an app could advise on the best microphone choice and positioning to make a 'warm' or a 'bright' recording of a cello in a particular environment.
The data on which the findings of this project are based are available in the following repositories.
- Multi-Angle, Multi-Distance Microphone Impulse Response Dataset doi: 10.5281/zenodo.4633508