A digital processor system obtains at least one time-domain signal representing brain activity and at least one time-domain signal representing heart activity, each having a time-varying signal value. The system produces representations of a plurality of acoustic signals, each of which corresponds to a respective time-domain signal and is produced by concurrently generating a plurality of acoustic parameters, including a plurality of time-varying acoustic parameters. One or more of the plurality of time-varying acoustic parameters is modulated in accordance with at least the signal value of the respective time-domain signal. Each representation of an acoustic signal of the plurality of acoustic signals is further produced by combining the concurrently generated plurality of acoustic parameters to produce the representation of the acoustic signal corresponding to the respective time-domain signal. The system combines the representations of each of the plurality of acoustic signals to produce a combined acoustic signal.
