Hum - Can you hear it, even if you can't hear it?
There's a similar parallel with low-level sounds in a mix. If you can't be sure that you can hear these sounds, probably because they are masked by higher-level sounds, then can you perceive them subliminally, and do they make a difference?
Here's an example pointed out to Audio Masterclass by Royjohn Wheelock. You'll need to listen to it because nothing here will make sense otherwise. Royjohn says this...
"Here is 4 seconds of Dangling Conversation by Paul Simon off the Parsley, Sage, Rosemary and Thyme CD. Do I hear a hum in there? My friends hear nothing. I'd like to have some trained ears tell me what I'm hearing. I'm listening with a pair of Grado Labs SR80 headphones through the audio output of a Lenovo T400 laptop with the Conextant HD audio codec and running Windows XP. Also this is only the left channel of that track - switched to mono so it is in both headphones."
Well I've listened several times and I have to say that I don't hear a hum. I feel that there is a hum present though. Perhaps there was a 60 Hz hum and the actual 60 Hz component has been filtered out, leaving a residue of harmonics at 120 Hz, 180 Hz, 240 Hz, etc. Indeed, if one looks at a spectrogram of the track, it is just possible to discern a tiny peak around 180 Hz, but of course that could easily be in the music.
What I do hear however is lots of atmosphere and texture. This isn't a clean recording by any means, but somehow it has an 'alive' feeling to it, rather than the clean-but-sterile recordings we often hear these days.
Whether a similar texture could be achieved with the hum generator plug-in I proposed recently remains to be seen.
But what do you think? Is there a hum? Would this track be improved with modern recording techniques? Let us all know what you think in the comments section below...
By the way, it is often possible to gain insights into recording techniques by listening to one channel only of a stereo recording. You'll hear things that you didn't notice when the other channel was playing. Then listen to the other channel and see what else you've been missing.