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In Reply to: RE: The CX-7e does not use op-amps posted by wormturns on February 7, 2009 at 15:34:29:
>> rather enthused about the MP filter <<
We are too, now that all that hard work is done!
We had originally planned to listen to the filterless "non-oversampling" designs many years ago. Unfortunately circumstances prevented it at the time. It turned out to be a good thing in the end, though.
The original impetus for listening to the digital filters was simply to check out the "non-oversampling" option and compare it to our existing filter. But then we decided to also listen to Peter Craven's "apodizing" filter. After that, the project took on a life of its own as we kept thinking up new ideas to try out -- it was months before we finished.
Even when we *thought* we were finished, we realized at the last minute that there was one configuration option in the DAC chip we hadn't listened to. This realization occurred the afternoon before we were packing up the entire soundroom to go to CES. So three of us dropped what we were doing and met down at the factory to do some listening tests. We ordered a pizza and ate there while we were listening. When we finally finished at 1:30 AM, we were pleased with the work that we had accomplished. But one of the crew (Ariel Brown, Ayre's "secret weapon") only got about 3 hours of sleep before he had to get up and pack for the road trip to Las Vegas...
But if we had listened to the "non-oversampling" years ago, we could have only compared it against the off-the-shelf digital filters. At that time we didn't have the tools to make our own custom filters using the DSP capabilities of the FPGAs. Plus we knew about, but didn't have the software tools to design the "minimum-phase" digital filters that turned out to sound better than the standard "linear-phase" filters. All of the filter design software packages just assume that everyone *of course* wants "linear phase"! This feature was only recently added to our software package, a $2,000 tool.
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Follow Ups
- RE: The CX-7e does not use op-amps - Charles Hansen 16:23:36 02/07/09 (0)
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