The Front End Holds the Line: What Heart-Sound CNNs Lose When Models Shrink
TL;DR for operators A team shrinking an audio classifier for a low-cost screening device has more than one place to spend scarce compute. The network can stay larger, or the input representation can do more work before the signal reaches the network. That trade-off became visible when this heart-sound CNN was reduced from three convolutional blocks to two. Using a plain log-mel spectrogram, modified accuracy—a score that gives equal weight to abnormal-case sensitivity and normal-case specificity—fell from 0.910 to 0.826. With a front-end that normalizes each frequency band against its recent energy so locally unusual sounds stand out more clearly, called PCEN, it fell only from 0.915 to 0.894. A front-end representing the same sound at several time-frequency resolutions, called multi-resolution log-mel, similarly fell from 0.916 to 0.894. ...