Timbral Characteristics of Off-Axis Microphone Response

Research Student: Juan Carlos Franco Hernandez
Principal Supervisor: Dr Tim Brookes
Co-Supervisor: Dr Enzo De Sena
Supported by: Doctoral College Vice Chancellor's Studentship Award

Start date: 2019
End date: 2022

Project Outline

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 is currently being 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 will soon be experimentally tested using controlled acoustic measurement of a selection of microphones and sound sources. Previous studies suggest that measurements should be made with an angular resolution of 10° or 15°. Appropriate measurement/recording environment(s), sound source types and source-to-microphone distance(s) are yet to be determined.

A combination of literature-based research and experiments using human listeners will then be undertaken to establish the impact of all of the above on the perceived timbre of sound captured by a microphone, and to 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.