…and for that, we have recording and mix engineers to thank. Thank you all for everything you do!
On the recording side, a well-placed stereo pair capturing an ensemble performance conducted and played impeccably can provide the holographic sound stage we’ve been discussing.
However, with most music being recorded with close mics on individual performers, the mix engineer has his or her hands full when it comes to recreating a lifelike sound stage. That is what we will dip our toes into this week: Engineers: Controlling Mix Imaging.
What are We Trying to Model?
This may be obvious to many of you, but let’s start with some basics. Imaging with solo performers is a no-brainer. For groups, we want to create a sound stage that corresponds more or less with the typical physical arrangement of the musicians. Here is a generic stage plot for a basic five piece rock/country band.
You see we have a singer in front with an acoustic guitar, an electric lead guitar behind and to the left, the fairly wide trap kit straight behind the singer with the electric bass right next to the drums. Finally we have a backup singer playing piano in front off to the right. So this is the sound stage we might want to recreate in the mix.
How is it Done?
Here is an example of a stereo image mix. Position A is created by sending both speakers the same loudness signal with no time delay. That’s the easy one.
Stereo position B is achieved by adding some time delay to both channels and reducing the loudness on the right side less than on the left side. This brings the object out of prominence (quieter) and rearward (later) while shifting to the right (amplitude ratio of dual sound sources).
For mono tracks, the pan knob allows amplitude ratio adjustment. The fader or allows level reduction. Time delay can be accomplished a number of ways in the digital realm, but keep in mind that sound travels about 1 foot per millisecond.
What is the Proper Range?
Image adjustments occur by adding time-delayed and volume-reduced versions of the direct signal. The volume range is about -5 to -20 dB and the delay range is about 0-5 ms to create a large, immersive sound stage.
Sometimes a mix needs to be a little “fuller” to invoke the extreme immersion that a certain song or band warrants. Maybe there are relatively few instruments, or maybe you are just looking for a massive wall of sound. Try these tricks, but always remember to honor the band’s intended sound faithfully. A little bit can go a long way!
varying time delay in the left and right channels for a sweeping, slightly angled image
duplications of tracks with different time delays and L-R balance
alter the time delay and L-R balance of reverb/FX tracks
invoke negative time delay! (be veeery careful with that one…)
What About the End Users?
And What About Acoustics?
Not only do recording engineers move images around, HiFi setups also can move images. We’ve been discussing the ways to do this for the last several weeks, but it is worth repeating a few key concepts.
Early side wall reflections move speaker positions to the sides (localization via precedence) and back away from the listener (time delay), creating a more distant and darker center image. To reverse the effect and experience what the engineer intended, place TubeTraps or StudioTraps in the signal paths.
It comes as no surprise, then, that adding time delayed low level center reflections will also create a change in the center image. The reflections boost the perceived level of objects centered in the mix. As this is the shortest path of any reflection in the room, the image location is locked dead center and prominence remains for our star singer or soloist.