The audio core is the frequency range which the human ear finds most sensitive, between 2kHz - 5kHz.
In 1933, Harvey Fletcher and Wilden A. Munson conducted the first research on the frequency response of the human ear. They played a series of tones to determine the listener's perceived loudness at different frequencies. The results showed that the frequency response of the human ear is non-linear. The perception of different frequencies also varies based on amplitude. Their research was used to create the Fletcher-Munson curve. This graphical representation shows that the human ear is more sensitive to the audio core than other frequency ranges. This makes balancing the core a critical aspect of mixing music.
Many other equal loudness curves have been created since these tests. The ISO 226 standard is now the most accepted Equal Loudness Contour. This is model is based on the Robinson-Dadson curves.
Mixing within the Core
It is an audio engineers job to balance the audio core.
In the past, engineers have used NS-10's to listen in more detail. Many engineers say "if a mix sounds good on NS-10's, it will sound good anywhere." This is because these monitors cause engineers to focus on the audio core.
NS10's may work for some applications, but they aren't optimized for core listening. They introduce a variety of distortions and aren't accurate for mixing bass. Engineers need to listen to the core in the most accurate way possible.
Reveal is the first plug-in developed for corelistening. It features a set listening filters which allow engineers to focus on the core and preview how their mixes will translate. Using Reveal, engineers will be able to craft amazing mixes that translate accurately to all speaker systems.
The Core Production Workflow optimizes translation for all speaker systems and devices. Often times a mix will sound great in the studio, but not when played on consumer listening systems. This is due to a poorly balanced audio core.
Place Reveal on your DAW's master bus. Turn on Critical Listening mode when making EQ and level adjustments. This will ensure that you are making the most accurate adjustments possible.
Listen to your mix with Critical Listening enabled. You may find that your bass instruments have almost disappeared. If this is the case, place LowLeveler on your bass instrument. Make adjustments to the Upper Bass (Harmonic) portion, then turn off Critical Listening mode. Now adjust the Low Bass (Fundamental) portion. Mixing in this way ensures that your bass is harmonically balanced and will translate accurately to all playback systems.