If this is true, then a brief 30s audio signal would yield more then a A4 photo capture of high density visual encoding, like microsoft hccb barcodes, interesting
A .wav file is 16 bits/sample x 44,100 samples/sec ≈ 700 kbps. Thirty seconds of that is about 2.5 Mb, which is a reasonable size for a photo. However, you wouldn't be able to send nearly that much data, since you'll be limited by various kinds of noise.
