How differences in stereo perception between studio monitors and headphones affect panning decisions . . . or do they?
When approaching a mix, the first area of concern should be dealing with gain structure, setting basic levels, and panning, ahead of EQ, compression, and effects. In the previous post, we discussed equalization before panning, since the frequency response of headphone transducers is the major area of concern when mixing with headphones as opposed to speakers. Another fundamental difference between the two, but possibly not as mix threatening, lies in our perception of the stereo field.
Better Hearing Through Headphones
You might wonder why, in the early days of stereo, mix engineers went to so much trouble to create a dimensional stereo mix, particularly when what they heard in the studio was never going be heard the same way on the available commercial playback systems. The reason was headphones.
In 1958, jazz musician John C Koss invented the first stereo headphones so that home listeners could get the most out a newly burgeoning technology called, “LPs.” As music grew in the ’60s to become the most dominant force of expression for a generation, the use of headphones grew along with it – particularly when it was discovered that headphones and certain natural substances provided a most unique and immersive listening experience. Today, headphones and ear buds have taken over as the primary listening medium, which alone makes a good argument for mixing on headphones.
Perception and the Illusion of Stereo
As sound researcher, Dr. Richard Heyser* said; “The actual sound field in a listening environment is not identical to the sound field which we may perceive…” He also went on to say, “If we wish to understand how to ‘measure’ what we ‘hear,’ then we must deal with subjective perception and the illusion of sound.”
Dr. Heyser’s observation particularly applies to the difference of stereo perception between speakers and headphones. Due to cross-feed, which is sound from a speaker on one side of the stereo field reaching the opposite ear, we perceive the stereo field at approximately a 60-degree angle from center position to left and right speaker (see the image below). Headphones eliminate cross-feed, so that our perception of the stereo field is 180 degrees, which in turn causes us to perceive the center image inside our head. While it may be argued that the isolation of headphones makes for an unnatural listening environment, keep in mind that stereo coming from speakers is a non-reality as well. At the end of the day, all we really have with stereo speakers are left and right. The center image and everything in between is a ghost that becomes less substantial as you move between speakers.
Since we perceive stereo sound differently in headphones than in speakers, conventional wisdom suggests that one might pan instruments differently, or even improperly, but it really doesn’t have to affect your panning decisions. Experienced mixers make panning choices based on a pre-imagined soundstage, not the geometry of speakers. They “see” the left-to-right position of instruments in their head and then make the appropriate panning choices.
A Panning Schema That Transcends Monitoring
There is a panning scheme used by professionals that completely obviates concerns regarding panning decisions in either medium, which is LCR (left-center-right) mixing. LCR mixing consists simply of panning all elements of a mix left, center, or right. LCR mixing has been a component of hit songs for decades and continues to be. For example, The Beatles “Strawberry Fields Forever,” “A Day In The Life,” and Jimi Hendrix’ “Purple Haze” are examples of LCR mixing. A-list mixer Chris Lord-Alge also mixes in LCR.
The only exception in LCR mixing would be panning to mid center-left or mid-center right in the case of background vocals or certain percussion instruments. Mid center/left and mid center/right are products of level differences between left and right, and as such, as we move closer to one speaker or the other, instruments panned there lose their position in the stereo field, sounding as though they’re coming directly from the speaker you’re closest to.
With large-format analog consoles, apart from issues of perception based on position between the speakers, the variances in the response of pan pots made accurate mid-left and mid-right positioning difficult. To overcome these inaccuracies, precision panning was achieved by sending a sine wave to designated left and right channels and adjusting the pan controls until the levels matched.
These days in DAWs, precision panning assignments are easily made numerically. However, physical movement between speakers can still obscure the results, particularly if you’re working in an untreated environment. Therein lies another advantage that mixing in headphones provides; you take the sweet spot with you wherever you go. What this means to the headphone mixer is that you can more easily get the same stereo results you would have to work harder to achieve with loudspeakers. You can also hear the end game of your panning as you work.
An important difference between mixing with monitors as opposed to headphones is our perception of the stereo field. Stereo perception can affect panning decisions if you base them solely on what you hear in either medium. However, if your panning scheme is based on a soundstage you imagine, i.e. putting the instruments on a virtual stage in a virtual space, your results will be unaffected by the playback medium (but you will perceive them differently). If you go with LCR (left-center-right) panning, the difference in perception between monitors and headphones is irrelevant, as long as the mix works.
* Dr. Heyser was the inventor of time delay spectrometry, which measures the response speakers in real-world environments.
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