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Old 7th March 2003, 08:27 PM   #11
jean-paul is offline jean-paul  Netherlands
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The so called very steep "brickwall" filters ( 100 dB was not an exception ) are supposed to be THE reason that the first cdplayers sounded so bad. From experience I can tell I never heard a cdplayer with a brickwall filter that sounded even good or satisfying. Phase behaviour was terrible too. But the so-feared RF did not pass through the interlinks !

Digital filtering wasn't invented for nothing. Cheaper than the tuned coils in de brickwall filters, occupying less space on the PCB and no necessity for manually tuning the coils. Better phase behaviour because of the simple mostly Bessel filtering that could take place now.

But with oversampling/digital filtering jitter-sensitivity has become more prominent than before.

Since I play around with non os DAC's I slowly get the feeling ( not more than that ! ) that because the jitter-sensitivity is lower sound immediately is better also. I don't have the sophisticated equipment to measure this, that's why I assume this. Even listening without any filtering ( don't do this at home ! ) is bearable too. Why did the engineers fear the very small RF output so much ? Soundquality really is better without steep filtering with some DAC's. Not all of course.

Sidenote: when I compare old 4 Fs cdplayers that are well modified with Bitsream/Mash/1 bit/high Fs cd-players and DAC's they win quite a few times in terms of soundquality and imaging. I know this is comparing pears with apples but it is fun to do

If you want to try these filters ( old thread only just reopened as I saw after posting ) the cheap way I recommend to wreck a very old cdplayer ( with 16 bit Linear written on the front ). Just cut the board where the filter with the surrounding circuitry is. You'll have a tuned brickwall filter with I/V convertors that works well enough for testing. A bit better opamps won't be a luxury since most of them used NJM4558's.

The LTC1562, which seems a very interesting chip, may be more expensive but it is far more flexible if you plan to roll your own brickwall filter.
It's only audio. Member of the non modular PCB design committee
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Old 8th March 2003, 12:11 AM   #12
fdegrove is offline fdegrove  Europe
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Scuse me, I haven't gone to the entire thread.

The so called very steep "brickwall" filters ( 100 dB was not an exception ) are supposed to be THE reason that the first cdplayers sounded so bad.
One of the reasons surely.
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