The last few weeks we explored moving the perceived source of a sound image along both the “Y-axis” (up and down) and the ‘Z-axis’ (from downstage to upstage) as ways of helping the audience achieve a better sonic placement of performers and instruments. This type of adjustment can be accomplished by manipulating the signal delay of each sound source and each speaker system so it aligns to or precedes the sound emanating from the sound reinforcement system.

We can control the horizontal axis

Traditionally, we have all learned to use Pan-Pots to control the perceived placement from left to right in the stereo image. The term comes from ‘Panorama Potentiometer’. The control adjusts the relative volume level of the audio signal feed to the left and right channels. The louder channel draws the listener’s attention and creates a sensation that a voice or instrument is somewhere between the two speakers.

In more sophisticated systems they have special pan-pots that control a feed to the center channel, too. These are called LCR (Left Center Right) pan-pots, and in the center position the left and right channels are still equal in level, but they are significantly lower than in a traditional stereo pan-pot, and the center channel level is at its maximum. When the LCR control is panned full left or right, both the opposite channel and the center channel are at minimum output.

Modern digital control consoles will allow you to tie a signal delay to the pan-pot function, and you can increase the delay of the opposite channel from the one that is being emphasized with volume. The Haas Effect tends to steer the brain towards the louder channel with the least delay. You don’t have to adjust the volume as much, if at all, to effect the image localization, so the entire audience area still hears the sound but thinks it is arriving from a shifted location. In conventional LR Stereo speaker layouts, the audience on the ‘away’ side of the pan tends to loose-out because the volume of that part of the program is attenuated.

Here is a good audio demonstration of this effect (best if listened to on headphones).

The audience members seated in the front few rows of the theatre / church / auditorium tend to suffer the most from speakers being mounted almost directly overhead. As you sit further back from the performance area the relative angle between the performer’s mouths and the loudspeakers is reduced, so the problem is less noticeable.

Picky, Picky, Picky

In the interest of accuracy and all common street semantics aside, the correct term for a control that adjusts the volume level between several sources or destinations is a ‘BALANCE’ control. A true ‘PANORAMA’ control really is a signal delay based effect because it is the difference in arrival time between our two ears that cues the brain as to where, laterally, the sound source is located.

It’s magic I tell you, pure magic. (Any sufficiently advanced science appears as magic to a lesser advanced civilization.)

In reality, the perception of sound is much more complicated than just time and volume – it involves the shape of our outer ears (the pinna). The shape of the pinna shifts each frequency in amplitude and phase as a source moves around us. This can be modeled mathematically and converted into a Pinna Transform, which in-turn can be encoded in an audio stream. I am unaware of any mixing console or console software plugin that would allow you to do this in real-time, however, it is probably on someone’s app list to be written. To get a better understanding of this effect visit this web site and play the demo tracks while wearing some headphones: www.audiocheck.net/audiotests_ledr.php

Freaky, isn’t it?

This test is also useful to see how well your control booth or home studio is designed and implemented. If you don’t clearly hear the sound moving around in the described manner when you play this back through your speakers, it means the playback system and/or the room surfaces have some very non-linear characteristics and are coloring your mixes.