This article is originally part of my book Electronic Projects from the Next Dimension – Newnes – 2001.
Basic configuration: using an audio amplifier (any of your sound equipment), you can fill an ambient with white noise or pink noise and let your tape recorder record with a microphone to pick the voices. Figure 1 shows how the experiments could be performed.
Make sure that the white/pink noise generator is plugged to the auxiliary input (AUX) and that the noise level is adjusted by the ampliíier and by the generator (if available).
If you are using a stereo amplifier, you can use two noise sources as shown in Fig. 2, plugging them to both channel inputs (left and right), or use one input using the amplifier in the MONO option.
A germanium diode such as the 1N34 can be added to produce a special effect, rectifying the output of the white/pink noise generators signal as shown in Fig.3.