# A Feasibility Study for a Hand-Held Acoustic Imaging Camera
## 3 Dual Cam Acoustic Camera  
We provide an overview of _Dual Cam_, an acoustic camera prototype developed at the Italian Institute of Technology [10; 18]. It combines a co-located planar microphone array and video camera for aligned audiovisual imaging, as illustrated in Figure 1. The current implementation utilizes a 0.5 \(\times\) 0.5 m\({}^{2}\) 128\(-\)element microphone array fabricated on a custom-printed circuit board working over wideband [500-6400] Hz. Each microphone output is digitized and processed in real time by an embedded system that performs beamforming over an azimuth-elevation scan region, where (\(\theta\), \(\phi\)) equals (90 \(\times\) 360) degrees. This generates acoustic images registered to the synchronized video feed, enabling visualization of spatial sound sources. However, the large form factor makes the device cumbersome for portable applications. Our goal is to significantly miniaturize the system while retaining imaging fidelity. Reducing the form factor exacerbates grating lobes and limits low-frequency coverage. Advanced optimization of the layout and beamforming filters is necessary to recover imaging performance on smaller scales through irregular configurations with microphone positioning tailored to the sensors and frequencies of interest. Acoustic imaging systems utilizing microphone arrays enable novel techniques for localizing and separating multiple simultaneous sound sources. However, real-world deployment remains limited given the unwieldy equipment required. The array's 128 microphones are strategically positioned using an optimized irregular layout [18; 19; 35; 36; 37; 38; 39] to synthesize directional acoustic images of the sound field when paired with beamforming algorithms [40] (Figure 5). These acoustic images represent spatial auditory information by mapping frequencies to pixels corresponding to locations. While originally high-dimensional, the key acoustic data can be compressed into perceptually relevant mel-frequency cepstral coefficients to reduce computational costs [41] (Figure 5). Studies demonstrate acoustic images can boost model performance by transferring spatial representations to improve audio classification accuracy. The addition of spatial audio details also helps disambiguate sources and generalize to new datasets [42]. However, real-world systems may lack these imaging capabilities. This work examines methodologies to distil the benefits of acoustic images even without access to specialized hardware. Optimized planar arrays provide more accurate spatial audio details compared to individual microphones by sampling sound fields from varied directions. Advanced beamforming techniques enable directionally focused listening to isolate specific sources in noisy scenes. Processing multi-microphone signals remains computationally intensive, though emerging algorithms and parallel computing facilitate real-time performance. The filter-and-sum [3; 43] beamformer synthesizes an array of impulse responses to steer directional sensitivity. While specially designed microphone arrays can provide valuable spatial auditory images, this research investigates generalized approaches using array signal processing to improve audio sensing tasks without access to imaging hardware. The filter-and-sum beamforming algorithm is a method for synthesizing the finite impulse response (FIR) coefficients [17; 25; 43] for small-sized two-dimensional microphone arrays [19]. This method can be used to generate acoustic images by focusing the array on a specific direction in space and enhancing the signal coming from that direction. The live acoustic imaging pipeline consists of:  
1. Digitizing microphone outputs through multichannel audio sampling. 2. Partitioning the multichannel record into short time frames. 3. Synthesizing beamformer filters according to designed array geometry. 4. Applying filters and aligning signals for each scanning direction. 5. Coherently summing aligned microphone channels to obtain beam pattern power. 6.