View Single Post
  #7   Report Post  
Greg Berchin
 
Posts: n/a
Default

On 29 May 2005 21:28:41 -0700, wrote:

Since those preprints are not free to download, can you tell me in what
way it is relevant to my question ?


Well, I figured that the title -- "Perfect Reconstruction Digital
Crossover Exhibiting Optimum Time Domain Transient Response in All
Bands" -- would be a good hint.

In your original post, you said:

could you synthesize the same
summed electrical response (and therefore the on axis response) in
terms of amplitude and phase response if you were to lower the Q of the
high pass section, and raise the Q of the low pass section from their
standard 0.707, without changing anything else ?


[...]

Some classes of high pass and low pass filter have ringing at their
crossover frequency whose phase is opposite to their complementary
filter


[...]

It occurs to me that this cancellation of ringing only occurs on axis,


[...]

With the output from the low pass section unable to balance the output
from the high pass section in these off axis directions, the ringing
will not be canceled.


In the AES paper, I address exactly this problem. First, the lowpass
and highpass filters are perfectly complementary -- that is; their
responses sum to unity magnitude and linear phase (pure delay) at all
frequencies. Second, their responses are in-phase at all frequencies,
so there are no off-axis anomalies. Third, ringing is eliminated
because the filter upon which this system is based is Gaussian (or a
Bessel approximation to Gaussian).

Has anyone tried something like this ? Any gaping holes in my idea ?


Basically, it lends itself only to digital signal processing, because
there are time delays inherent in the technique. Implementing pure
delay in analog electronics is difficult.

Greg Berchin