Question about the Haas Effect

Question

I'm reading an interesting article about incorporating the 'Haas Effect' during the mixing stage of a song but I can't understand the following extract:

“The Haas trick adds to the standard panning method time differences, and with a filter on the delayed channel we can also tuck on some frequency differences. However, this application is limited to instruments already panned to one extreme – we cannot pan the original signal anywhere else.”

Please note, I did a lot of reading yesterday about panning laws, stereo vs dual mono vs balance so maybe I’m simply confusing myself:

So I understand you can’t pan a mono signal but only change the balance. So if you duplicate this mono signal into a dual mono track; what does he mean by "this application is limited to instruments already panned to one extreme"? Does he mean that, for example, the left channel should be panned to the left extreme and then the right (delayed) channel panned to the right extreme and only then you can change the frequencies of the right channel? What confused me most was when he said "we cannot pan the original signal anywhere else". But what if you panned it back to the centre and kept the right delayed channel at the right extreme?

I've absorbed so much audio theory lately so my brain keeps confusing concepts.

SOURCE: http://audioundone.com/the-haas-trick

Answer 1

His wording is confusing, but he does mean that the two channels, the original and the duplicate, should be panned hard left and right. The whole point of using the Haas effect is to maintain the even levels of a mono signal, but fooling the brain into locating it either left or right.

I’m not sure if you understand how the Haas effect works or not. I’ll describe it here. If you already understand it you can ignore that part. But understanding what is happening is key to knowing how to use it.

Your brain uses three different cues to determine the direction a sound is coming from: amplitude, Haas effect and frequency spectrum. Turning a pan knob does the first (i.e. sound coming from the left will normally be louder in the left ear).

Say someone is standing in front of you and hits a wood block or something. That sound will arrive at both ears simultaneously. If that person moves to one side or the other the sound will arrive at the closer ear a couple milliseconds before the other. Your brain will interpret this difference in arrival time to locate the source of the sound.

Secondly, that sound will reflect off of other objects, walls etc. causing an even longer delay. Your brain knows to ignore these reflections when locating the source of the sound. After a certain amount of delay, though, your brain will begin to interpret these as distinct echos coming from a specific direction. So the Haas effect is limited to a certain delay setting. (The article author mentions 35ms.)

The Haas effect can even override the amplitude difference. Say you’ve got cotton in one ear, muffling sound. You can still tell what direction sound is coming from even if the wrong ear hears it louder. That’s why the author of the article suggests it as a way to seperate instruments without having to pan them off center.

The third thing that affects sound locating is frequency spectrum. Normally the sound arriving at the ear toward the sound will have slightly more high frequencies than the opposite ear. Basically the opposite ear will sound a little muffled. When the author of that article talks about filtering he is meaning rolling off a little high end on the delayed copy to enhance the Haas effect.

Haas effect works fairly well in headphones, where the two ears are completely separated. In stereo speakers the effect is less pronounced, especially if you are not centered between them, but it can help to create more space in the mix. It also works best on percussive sounds and less so on things with a more even envelope. It also works better on higher frequencies and less so on lower ones. So, nice for cymbals but not so much for bass.

As an aside, frequency response actually goes even further in locating sound. This is actually the reason the pinna of your ear (the big thing that sticks out the side of your head) has the unusual shape it has. Sound reflecting off the different folds of skin will effect the frequency response of the sound differently at different angles. Your brain uses these differences to sort of fine tune the direction a sound is coming from.

These specific frequency response differences are super subtle, so they’d go beyond the ability of using it for mixing. But I once heard a demonstration of this effect in headphones. The person who made the demonstration had made a fake head with a microphone positioned where the eardrum is, then modeled all the different frequency effects. In headphones they could use this to place sounds at very specific locations around the listener.

Answer 2

I think you're complicating things a bit there. The Haas Effect is a psychoacoustic effect. It takes on the principle of delay as a way localizing the source of whatever we hear. Don't over think things over.

Basically you have two tracks (on is the copy of the other): One is fully panned left and the other is fully panned right. Apply delay for 30ms (give or take, this is a matter of experimenting) to one of them, doesn't matter which, or drag one of the clips (if the case) a few milliseconds do the right (or left, whatever you choose), and you should immediately start to hear the difference.

Please note that this is only practical with MONO recordings as the source is already "summed". If you have a Stereo recording (XY, ORTF, MS, whatever), fully panning the whole clip to one side will sum all the sounds in the recording. Basically you'll loose perspective, and most os its frequencies. Imagine playing back a Stereo recording of some sort, and on your monitor settings you set it up to MONO: you'll immediately notice some elements are missing. Thats what will happen. BUT, if you pan a MONO recording, you won't loose any information at all.

Hope this helped. I'm not a teacher, not by a long shot, so I hope this wasn't too confusing.

Cheers