The product is placed in a room typical of the environment where the product is normally used. The product is used and recorded via a microphone onto a digital recorder such as DAT tape. From there the sound is taken into the computer via a sound card. Once on the computer, the sound can be manipulated using commonly-available music processing software. Then the sound samples are blasted onto a CD for later reproduction The sound is then reproduced over headphones to the listener who then makes judgements on the sounds using a questionnaire.
There are many variations on the set up suggested above, but this is one of the most common.
It is possible to listening to one product after another "live" without recording and reproducing the sound. However, this causes many problems. For a washing machine, for example, the wash cycle is far too long for people to sit through. Even with products that have short sounds, the delay between auditioning products that happens in such "live" tests mean that the subjects' judgements become more unreliable when comparing products. There are also products where it is difficult to ensure that each listener gets to hear the same sound because the sound is different each time the product is used. It is also important that each product is played from exactly the same position in the room, otherwise the sound is affected by the position, and so it is necessary to swap over products so they are played from the same place, and this is a slow processes for many products. For these reasons, it is best to record the sounds for later reproduction.