What is the sound you hear during the "silent" moments of a video or audio recording?

I’m using this video as an example because the audio cuts out several times, and you can clearly hear the difference between the completely silent moments when the audio cuts out, vs. the quiet moments when there is no sound in the room but you can still hear the hissing sound / white noise on the recording. You can clearly hear the difference between the the hissing sound when there is no sound in the room, vs. the complete silence when the audio cuts out. What, specifically, causes this hissing sound (or white noise)? Low quality equipment?

(Some may find the video more interesting than my question.)

Could be a recording with white noise in it, but couldn’t it also be that there is actually a sound in the room, like air conditioning?

If you recorded yourself sitting at the computer right now, it would probably be pretty noisy. The noise in this vid could be the air conditioning or perhaps the lab’s ventilation hood, sound from outside via an open window, or even the self-noise of the microphone/amplifier. This recording likely has one microphone sitting in the middle of the room.

You can hear that the experiment’s conductor is a fair distance away from the source, and that the glass sounds are very clear. For the speech to be audible, the mic’s preamplifier would have to be turned up quite a ways. It thus amplifies quieter background sounds in the room (A/C, wind, a fan) by just as much as the speech, making them, obviously, quite loud. It actually sounds as if the audio has been amplified digitally (i.e. after the original recording), which can be an incredibly noisy process.

Silence is rather subjective. There’s plenty of noise in a ‘quiet’ room that we just ignore. The only rooms that are truly quiet require a lot of expensive treatment, especially to the AC, because most of this treatment traps heat. Oftentimes in audio engineering you’d just use a noise gate, which measures the minimum level you want to hear (in this case, the conductor’s speech), and shuts off the rest (hence the word ‘gate’).

Audio tape always has a little background hiss, caused by the magnetic particles that record the sounds. They affect the read heads as they go past just enough to register.

Dolby Noise Reduction was one method of reducing it.

If you’re already dead, and you crank up the volume on tapes of interviews with former patients, you can sometimes hear other dead people. Pretty weird.

…a tip we can all put to use! :smiley: