"Trevor Wilson" wrote in message
...

[snip]

**Indeed. What does one do? Here's what one SHOULD do:

One should buy a DIGITAL, zero phase shift equaliser (not possible with
"simple" analogue tone controls),

Many people consider this to be at least partically incorrect, myself
included.
ANY causal filter causes phase shift. It doesn't matter whether the filter
is in the form of a distributed L-C cable, or a room resonance, or whatever.
It does not matter what PHYSICAL FORM the filter takes. The modes of a room
constitute a causal filter, and it causes phase shift.

An analog equalizer, since it is also a causal filter, also has phase shift.
But when it is used to correct frequency response, it exerts phase shift in
the opposite direction of the anomaly that requires the adjustment. Thus, an
analog equalizer actually reduces total phase shift when used in reaction to
room modes.

On the other hand, room absorption at far-field distances does not
constitute a linear system integrated with the speaker. Consequently, high
mid and treble frequency response that is not liked by the listener might be
optimally corrected with a zero phase shift equalizer. But this begs the
further question, does this technique work very well? Many people feel that
correcting absorptive room response with an equalizer results in
subjectively worse sound, consequent to the fact that reflected sound is not
perceived in the same way as direct sound.

So whether phase shift in analog equalizers can be a reason to switch to
digital depends upon the details of the intended use. As I have remarked on
multiple occasions, there seems to be no FAQ on how a residential user can
productively use an equalizer. In most cases, the opportunities seem to be
limited to perhaps one or two low modes. In afew cases, the user may be
dissatisfied with a speaker response anomaly that can be smoothed over. But
the phase angle of the speaker at that point is tyically not known to the
user, still begging the question of whether to use a zero phase shift
instrument.

Perhaps there are other reasons people would like to submit, such as the bad
behavior of op-amps giving gain. But eq boosts have other problems as well,
with the amplifier, and drivers. Perhaps an all digital chain would be a
sufficient reason, but as I recall, most digital eqs are used analog
in/analog out.