How many times have you been working on a mix with the speakers cranked up, the bass is pounding and it sounds great, only to listen back to it later at a lower volume and to your dismay, most of your bass has disappeared and your mix now sounds limp and thin. This phenomenon is common and it has to do with how the human ear perceives sound at different volumes. Humans don’t hear every frequency with the same intensity (for the benefit of those of you who don’t know, the frequency response of our ears is commonly referred to as the Equal Loudness Contour). In a nutshell, it shows us that it takes far higher levels for very low and high frequecies to sound as loud as midrange frequencies, and that our hearing is most sensitive to frequencies from about 2 kHz – 5 kHz.
Great, but how does this affect the quality of your mixdown?
Just as the frequency response of you speakers plays an important role in how your mix sounds, so does the frequency response of your ears. For example: If you are mixing at 50dB SPL (sound pressure level), a tone of 30 Hz will need to be about 30dB louder than a 1 kHz tone in order for the two tones to sound the same perceived volume to you. Therefore, you may want to turn up the bass frequencies in your mix. When you isten back to it later at a lower volume, the bass will be overpowering. This also works if you monitor too loud. Since we hear low and high frequencies better at higher volumes, you might think that there is enough bass and treble when mixing, only to hear it disappear at lower volume settings.
So how loud should you mix? Well, an industry standard of 85dB SPL has been aopted in order to keep your overall frequency balance as constant as possible at different volumes.It is loud enough to be able to hear the lows and highs clearly, but not too loud so as to trick your mind into thinking that the bass is excessive. Some studios use a hand-held meter that the engineer can use to measure the sound pressure level. If you don’t have one, the volume of most movie theatres is about 85dB, so close your eyes and imagine you are at the moies and set your monitor volume accordingly. I can almost smell the popcorn now . . .
George Kourounis, Instructor, Sound & Recording Techniques, Trebas Institute.