Butterworth low pass filter
jowi -- Wed, 10/01/2008 - 06:55
Maybe nobody notified; but Accuphase is the first manufacturer in the world using a new kind of low pass filter in their CD-players; named after Steven Butterworth, who discribed this kind of filter maybe a century ago. Accuphase uses this 5 pole Butterworth filter in their new 800/700 and 500 series. Because of that, they do not over- or upsampling anymore, but the PCM data goes straight vanilla to the DAC's. The filter they developed is absolute free from pre- or after ringing.
The treatment of the (Super Audio) bit stream is even more interresting.
The 700 and 800 series do upsample the bitstream by factor 2 to 5,6 MHz and provide the 8 parallel DAC's delayed by one clockstep the same signal, they created for the first time in the world's in this way a high cut filter. These Japanese are really bright engineers, dont you think ?
Audio Note also had a DAC with no oversampling digital filter. I never heard it, but some reported that it had a wonderful purity in the midrange.
My recent experience suggests that conventional digital filters are to blame for much of what we call "CD sound." I've heard three digital products recently that employ very sophisticated custom filters running on DSP platforms, and they all sound far removed from CD. Those products are the Meridian 808.2 CD player, the Spectral SDR-4000 Pro CD player, and the Berkeley Audio Design Alpha DAC.
I'm reviewing the Alpha DAC in the January issue.
Dear Mr. Harley,
I feel very privileged that you personal did give a reaction on my Butterworth post. Monthly my bookstore in the Netherlands keeps the ''absolute Sound'' for me apart, as I also read your books. Most of all I appreciate your technical enlightenments about all kinds of subjects like you did for example "super" in Issue 174, in Feature & Tech. reviewing the overspoken Cambridge player.
Back to the Butterworth filter; physical ideal but a very complex and very steep (5th order means 5 x 20dB/decade is 100 dB = 30,1 dB/Octave) working filter, brilliant designed compared to the filter used in the also absolute sophisticated Meridian Reference 808.2, but hinders post-echo.
Believe me, the DP-700 does not sound digital, not even compared to my own DP-78.
I would appreciate if you spent an article about this forwarding technics in your magazine.
With kind regards - joep de vet
Thanks for the note. Perhaps we should review the Accuphase and Meridian and use the review as a platform for a discussion of the very different filtering approaches.
Thanks again for the kind words.
On the expo in Tokyo, Accuphase showed already the DP-400 and 600 series. The 400 player will be the new low end player, while the 600 will replace the DP-78.
Both new players are equipped with the fabulous Butterworth filters.
During the VAD show in Veldhoven (Holland) Accuphase importer from Benelux 'Paul Hattink' showed on a nearby dealer location the DP-800/801 combo. I had the prevelige to listen to this great € 26.000 player !
Magazine 'music emotion' reviewed in the october and november issue in a comparisation test, both the neutral Accuphase Combo 800/801 against the biting Estoterics P-03/D03. Reviewer 'Werner Ero' concludes that Accuphase CD sound is almost identical to both players SACD sound.
A shame on the VAD show was the disappointing Magico V3 (on Swiss Solution equipment) agressiv in the upper frequencies and no low end at all. Also disappointing on an Audio show was that Wilson Audio speaker range was only showed ? I really hoped to get a chance to listen to the WA Puppy 8 but it stays a dream.
The Magico V3 can sound bright with too much toe-in, and correct placement is essential to getting smooth and extended bass.
Awesome stuff.
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