Mono audio recording

What creates the illusion of depth of field in a mono audio recording?

Is that a theoretical or practical question?

Stereopsis is a function of binaural parallax: each ear receives input from a different acoustic perspective and the brain interprets the difference as depth – the same principle that allows us to see in 3D. A monophonic recording, like a two-dimensional photograph, contains information from only one perspective and is therefore perceived to be flat.

There are ways to massage a monophonic recording into something closely resembling stereo. The most convincing is a digital signal processing (DSP) technique in which the acoustic properties of a particular venue – a nightclub, say, or a cathedral – are used to reproduce the phase differences that would be present if the recording had originated in that environment.

When I listen to mono recordings it sounds like some of the instruments are at the edges (to the far left and right). While the other instruments and especially the vocals seem to be dead center is the middle surrounded by the other sounds. To describe the sound in a visual sense, it would look an upside-down V with the vocals at the top and middle and the other sounds going down and out.

My best guess is this has to do with volume of the individual instruments in the mix.

That, and the use of various effects (reverb, compression, EQ) that allow engineers to add punch to some tracks and bring them forward and have other tracks lay back.

What equipment are you using?

To be basic about this, what gives our hearing depth is of course two ears. If something is truly a mono recording, all sounds will come from one point. When I say truly mono, I mean recorded with one microphone, two a single source (not stereo media) and then played back on a single speaker. A single microphone will record the sum of all noise (more or less) without distinguishing one from the other. The single microphone will not give preferences to a singer. So if you record a concert, with a single monophonic microphone, you’d might end up with a recording of a lot of drums, and not much else. To get a feel for the limitations of a mic, plug up one ear, when in a noisy environment, and try to hear what someone behind you is saying.

So why does it sound the way it soes on your equipment? Without knowing the details, I can only venture some guesses:

  1. You recorded something on a minidisc, with only one mic, and played it back on your stereo at home. Generally, one should always play back on the same equipment one records. The disc/tape wobbles in diferent ways ASF. This can result in the recording coming slightly out of phase, giving it a faux depth.
  2. You’re using gizmo to playback, with lots of stuff that cheats. Typically smaller stereos for the average user, has filters and stuff to widen the sound coming from the (almost always) crappy speakers. This is typically done by getting the phasing a little off.
  3. Your speakers are connected the wrong way (check the plus and minus and the cords). Many people don’t notice this when listening to a stereo recording. When you play something in mono, the sound can become weird.

Once again - true mono will not have the depth/width you describe.

I am listening to The Beach Boys Pet Sounds (Mono Version) on headphones contected to an IBM ThinkPad.

When you look at a photograph of a person standing in front of a house you can tell that the person is closer to the camera than the house is. There are certain depth cues (occlusion, for example) that tell us we’re looking at two separate objects, while the brain projects its knowledge of three dimensional space to arrive at the conclusion that one of the objects is in front of the other.

I’m sure you’ve seen novelty photos where a person appears to be pushing two trees apart when in reality all three objects are in different positions? Or the Kids In The Hall “I’m crushing your head” gag where they close one of their eyes and peer through their thumb and forefinger in order to pulverize the skulls of passersby? These illusions work because, denied the parallax necessary for the brain to accurately perceive depth, it can be tricked into perceiving improbable physical relationships by applying three-dimensional rules to a two-dimensional image.

By the same token, if you listen to a monophonic recording there are certainly some depth cues to be heard there – the vocalist is louder than the percussionist therefore the brain perceives the singer to be ‘in front’ of the drummer, and acoustic reflections can still reveal environmental details such as whether the recording was made in a concert hall or a subway tunnel. Without a second channel to provide acoustic parallax it can’t reliably determine whether the keyboardist is standing to the left or the right of the singer, or whether he’s playing in front of or behind the drummer, but it can still work out approximate spatial relationships based on the depth cues that are there.

Well of course. If the singer is four inches from the microphone, and the pianist is a hundred yards away, the singer will be louder on the recording, even if it’s just a whisper.
However, having instruments show up to left and right and song on the middle is not a property of a mono recording.

Ihaven’t heard that album in ages. Listening on mono in headphones can be a little freaky, and if everything is connected properly, the sound should appear ‘in the middle’ of your head. Maybe a bad connection for the headphones? Those miniplugs and the whole where you connect them are notorious for bad connections.
Again - should you listen to the record on a single speaker, I bet you will not experience this, TJ555 The Golfer.

Let me clarify, nothing appears to the right or left. It appears to the right and left. For example on “I Just Wasn’t Made for These Times” the vocals seem to take up the whole head from left ear to right ear. Then when the tympani and bongos come in they appear to be in the center of my head and don’t “expand” all the way to the ears.

Of course not. You’d need a source of acoustic parallax (i.e., a stereo recording) to perceive that.

If you’re experiencing an impression of depth from a monaural signal, it’s because your brain is organizing your perceptions according to spatial cues present in the recording similar to the way it interprets spatial relationships between objects in a photograph.

Right. So what’s the question, exactly?

      • The typical way to get a full sound without reverb is to have the performer play or sing the exact same thing multiple times and re-record and combine the multiple recordings. Generally if you record something only once in mono it tends to sound rather “flat”, from either a single mono or stereo speakers. This might be what the OP refers to, might not.

How and why does, my brain do this?

      • Vell, eet ess zee seempeel ansvah of yor preoccupazion vit zee lunchmeats, because ven yoo ver a tinee lad yor mozza and fazza dvessed up as cows and vere beating you vit sausages.

I’ll just throw this out there, but Pet Sounds was issued in both stereo and mono, and also on the recent reissue all the tracks are repeated, first in Brian Wilson’s mono mix, and then in a remastered stereo mix. If you are listening to the CD itself, then you no doubt know which tracks you are hearing, but it is possible if you got the tracks from ehm a less reliable source, that you are in fact listening to stereo recordings. Just a thought.

Do a google search on psychoacoustics and browse your way to enlightenment. :slight_smile:

Try and find the Pet Sounds Sessions boxed set.

'Nuff said.