Listening broadband physical model for microphones: a first step

TL;DR

This work develops a broadband physical model for microphone directivity by decomposing the captured sound field into an omnidirectional component and a dipolar (bidirectional) component, showing that the classical directivity pattern $D(\theta)=m+(1-m)\cos\theta$ emerges as a limit case under monochromatic, low-frequency, and far-field conditions. The model is implemented as a real-time digital filter framework in Max/MSP, where the omnidirectional and bidirectional fields are combined via a directivity filter $H_{dir}[z]$ and a global transfer $H[z]$, incorporating frequency- and geometry-dependent effects. Key contributions include explicit digital formulations for the omnidirectional, dipolar, and bidirectional fields, a scalable design for a broadband directional simulator, and a discussion of extensions to include microphone transduction, room reflections, and proximity effects. By enabling perceptual listening with broadband sources (e.g., monophonic music) and proposing subband analysis as a more relevant evaluation tool, the work offers a practical pathway toward more accurate microphone modeling and design-guided experimentation, with potential applications in multichannel recording and spatial audio synthesis.

Abstract

We will present a first step in design of a broadband physical model for microphones. Within the proposed model, classical directivity patterns (omnidirectional, bidirectional and cardioids family) are refound as limit cases: monochromatic excitation, low frequency and far-field approximation. Monophonic pieces of music are used as sources for the model so we can listen the simulation of the associated recorded sound field in realtime thanks to a Max/MSP application. Listening and subbands analysis show that the directivity is a function of frequential subband and source location. This model also exhibits an interesting proximity effect. Audio demonstrations will be given.Paper 6638 presented at the 120th Convention of the Audio Engineering Society, Paris, 2006

Figures (4)

• Figure 1: Digital filter to apply to the source signal to derive an omnidirectional acoustical sound field.
• Figure 2: Definition of the geometrical configuration used to build the dipolar acoustical sound field.
• Figure 3: Digital filter to apply to the source signal to build a bidirectional acoustical sound field.
• Figure 4: Digital filter to apply to the source signal to apply an chosen directional acoustical sound field.