Direct digital-to-analog conversion of acoustic signals

We report initial experiments on voice-band acoustic transducers (receivers) designed to accept digital (pcm) signals and directly convert the received bits into analog acoustic output. We describe experimental designs for 4, 5, and 6-bit digital receivers and for an acoustic system that functions as the desampling filter for the decoded signals. We report measurements on the frequency response, amplitude linearity, and signal-to-quantizing noise for the digital receivers and show that these quantities fall into expected design ranges. Though relatively primitive in their initial forms, the transducers accomplish direct digital conversion with acceptable fidelity and suggest a further means for minimizing per-line equipment complexity in digital voice systems.