vTuning was a trademark name for our single knob adjustment of Crescendo corrections. It is a completely meaningless name, but it stuck. There is no “V”.
Here is an early paper on the topic.
Continued work on the topic has shown, across a survey of many different users, a range of slopes between 3 and 4 dB/Bark. The sonic differences are slight, and a good guesstimate may as well state that the rate of threshold elevation growth is 3.5 dB/Bark.
The effect I’m describing with vTuning can be likened to the damaging effects of a hurricane as one progresses further inland. Near its arrival at the shoreline, the damage is greatest. But that damage extracts power from the storm so that as it moves further inland, the damage declines.
When something declines as a percentage or portion of itself, that is a well known situation that describes an exponential decline:
When expressed in dB measure, this indicates a linear decline with distance.
Loud noise can be seen as an incident storm across the basilar membrane in the cochlea, producing the greatest damage where it first enters the cochlea at the oval window, and declining in its damaging effects as one progresses deeper along the basilar membrane.
Bekesey showed in the 1950’s that highest frequencies are sensed closest to the oval window, where sound enters the cochlea, and that bass frequencies are sensed toward the far end, called the apical end of the cochlea.
Hence the damaging storm analogy is fitting for sensioneural impairment, where impairment grows with increasing tonal pitch.
The rate of decline in the storm is that 3.5 dB/Bark. And Bark frequency measure corresponds almost one for one with linear distance along the basilar membrane. This rate of damage decline must be due to cochlear fluid viscosity and mechanical effects. It is very similar between individuals. And that is why vTuning, a single knob adjustment for Crescendo, works so well across so many different people.
That single knob simply tells Crescendo how much damage has been sustained at 4 kHz. The vTuning level is a best estimate of your threshold elevation at 4 kHz. And knowing the rate of decline to be about 3.5 dB/Bark, we can compute what it will be at all other frequencies.