Loudspeakers and the Tolerance Parameter

I’ve been using the term tolerance to describe speakers ever since I started using the excellent ATC SCM150s in the mastering room.  

What is tolerance as it applies to speakers? Well first of all, it’s a bullshit term that I made up, but basically it’s a way of describing how quickly a speaker will show you when you’ve made a counterproductive processing move.  So tolerant speakers have a wide window of acceptable sound, whereas intolerant speakers have a narrower range of acceptable sound.

For example, I have used (well regarded) speakers that would allow you to boost 3db at 4k on a given recording and sound fine.  Boosting that same recording 3db at 4k on the ATCs would immediately sound harsh. On the ATCs a boost of 1.5db was more appropriate.  

So what is correct?  

Checking those two options on a variety of systems in the real world reveals that on most systems, both masters sound very similar, and the 1.5db difference at 4k is mostly a moot point.  However, a few systems already predisposed to sounding harsh in the midrange revealed the 3db boost to be too much, and the 1.5db boost to be spot-on.  But critically, the opposite was not true - on systems with recessed midrange the 1.5db version was still good.  The conclusion here is that the lower tolerance (intolerance) of the ATCs allow the user to spot potential translation problems that would be overlooked on the other mastering speaker system.

To make matters more complicated, tolerance can vary by frequency - for example, some speakers may be tolerant to changes in the low end but intolerant in the highs.

All of this points toward the need to evaluate mastering speaker candidates for an extended period of time, and by doing real work with them.  

Just listening to speakers is not enough and won’t reveal their suitability (or not) for making mastering processing decisions.