Originally Posted by terry j
just a quick question on the ringing of steep filters (I won't go into audibilty etc).
re the deqx, it can go up to 300 db etc, but afaik even deqx does not recommend (usually) that steep a slope.
How steep is too steep? (with digital x-over slope I mean) I guess morbius would say 300 is too steep, but is 48 db too steep? 100?
This I guess relates back to the 'uncertainty principle' in audio? the more we tighten the FR the more we screw the time, and reverse. Is it all down to the individual case, where for a given set of drivers what works best is not the same as another set?
Verry good!!! There IS an "uncertainty principle" here. It is closely related to the
Heisenberg Uncertainty Principle in Physics - and the mathematics that dictates the
existence of these principles is the same. You can't know the position and momentum
of a particle simultaneously to arbitrary accuracy. The position of the particle is analogous
to the temporal response. The momentum of the particle is analogous to the frequency
response. If you attempt to determine the momentum to "perfect" accuracy - you
destroy the information on the position of the particle.
Likewise, just as terry states; if you attempt to be "perfect" in the frequency domain;
you are being inaccurate in the temporal domain.
Do we reckon Dave Wilson got his desired results in an afternoon?
If all Dave Wilson and company were doing is tweaking their crossovers in SPICE or
some other circuit modelling program; then they could get a result in an afternoon.
But that is NOT what they do. Dave Wilson and his engineers LISTEN to their product
and they make tradeoffs. They may allow a degree of non-flatness in the frequency
response curve in order to get a better temporal response. Dave and his staff are being
good engineers. They know FR is not some "Holy Grail" of audio quality that has to be
optimized at all costs. They are doing what all good engineers do in designing a product;
they are making tradeoffs.
Good audio engineers do that. They don't just "go by the numbers". They know what
the metrics like FR mean - and know the limitations of those metrics. In his review of
the dCS Scarlatti in the July / August 2008 issue of The Absolute Sound, issue #183;
review Jonathan Valin makes the same comment about the engineers at dCS. He
states they know the mathematics behind the workings of their processors; but that
they also LISTEN to them.
If an electrical engineer comes to me with an amp design that has vanishingly small
THD; it propably means he / she loaded the amp with tons of negative feedback as
was done back in the '70s. The engineer has designed the amp to measure well on a
THD test - but that's about all it will do well. The negative feedback doesn't allow the
amp to respond quickly to changes in the signal; and that's what the music demands.
We have an engineer that optimized on a SINGLE metric - and created a LOUSY audio
amp in the process.
Engineers can't be slavish to the metrics. There is no metric that measures absolute
audio quality. There a number that serve as guides to audio quality. However, if one
picks a single metric or a couple and optimizes on those; then that is NOT good