Adventures in DIY: All in a Phase Work

Do-It-Yourself Surround Sound
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Herbie Hancock’s answer surprised me. After seeing him play a Korg Karma, I asked if he used it to trigger unexpected riffs as a way to spark new ideas. “Actually, you know how we were using it?” he replied. “As a surround-sound-producing synthesizer, because it has not only a left and a right, but two auxiliary outputs. We’d construct certain sounds so that we were sending some components to the third output, and we sent that to the surround engineer. Then he would place them wherever he wanted in the rear speakers and the side speakers. It made the instruments sound huge.”

Herbie explained he typically would route the attack of a note to the front speakers and the body to the sides and rear. “We can also manipulate the sounds ourselves with the Karma’s sliders,” he said. “That’s a great feature in a surround environment, because we’re able to move the sounds from the stage.”

Fig. 1. Brian Eno’s suggested three-way, ambient speaker system, from his 1982 release Ambient 4: On Land.

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If your synth doesn’t have four outputs, a quick way to play with real-time spatialization is to run the headphone output through a reverb and send that signal to additional speakers. Brian Eno diagrammed another easy surround hack on the back cover of his recording Ambient 4: On Land. He set up a third speaker behind the listening position and wired it to the left and right positive (red) outputs of his stereo (see Figure 1). Called the Hafler Circuit, this setup drives the rear speaker with the difference of the left and right signals, which tends to emphasize ambience. DIY writer Rod Elliott shares refinements of the circuit at http://sound.whsites.net/project18.htm.

Another fun trick is to embed a surround signal in your stereo mix using an approach from 1980s Dolby Surround encoding (http://tinyurl.com/dolbys). This splits a monophonic surround track into two streams, offsets the phase of one by +90° and the other by –90° (putting them 180° out of phase), and mixes them into the left and right channels of the recording. On playback, a Dolby Pro Logic decoder subtracts the right channel from the left and sends the result, through a delay, to the surround speakers.

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Because I didn’t have an adjustable phaser handy, I simply duplicated a whispery vocal track and flipped the polarity of one copy in my audio editor. I then saved an MP3 of the mix to a thumb drive, plugged that into my Blu-Ray player, and dialed up the Pro Logic setting on my receiver. The whispery voices jumped out of the surround speakers. I can’t wait to try it with music.