Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems Stereophile Review of Meridian 808.2

Stereophiles review of the 808.2 is now up at their website:

http://www.stereophile.com/cdplayer...ference_cd_playerpreamplifier/index.html

Great review. Didn't have time to read the whole thing in detail.

But one thing that immediately caught my eye was the at length discussion of apodizing filter and how it helps restore problems from ORIGINAL A/D conversion.

So why is it that in the current context of discussion to date that the apodzing fileter is only applied if Meridian applies upsampling?

Am I missing something, did John Atkinson miss something (doubtful I know)?

I was going to post about the following last week after reading the print issue, but forgot. However:


So hopefully the G68 (and G61R to relate to the other thread) will be a candidate for upgrade. At only 6 channels in currently, that would be just 450 of the 900MIPS available - hopefully the remaining 450MIPS is good enough for MRC and 6->8 channel expansion.

I think I'd give up a bunch of MRC filters for it. I think I typically use about half.

Unfortunately, it doesn't quite work like that. Until the G68 "morphed" into a 900 MIPS machine from 750 MIPS, it was believed that 150 MIPS was available for upsampling on the receiver card with the other 600 MIPS reserved for DSP presets, time and level alignment, and MRC. So is the split now 300 MIPS and 600 MIPS? Not clear at all. Also, whilst the 808.2 uses a 150 MIPS chip, I doubt that all of it is used up.

Dear All,

Stereophiles review of the 808.2 is now up at their website:

It has been on Duncan's site for some time too.

Regards

Interesting review (now that I've actually read it). Lots of brownie points to the team from Huntingdon...

Regarding the 150 MIPS chip, I noted that it is used to upsample (and apodize) to 88.2kHz for the digital outputs, and is also required to upsample the 88.2kHz (conventionally) to 176.4kHz for the internal DACs. These would seem to be separate operations (I can't see how they could be combined), so apodizing a stereo signal will require considerably less than 150 MIPS.

The discussion of eliminating artifacts from the original A/D conversion is not a function of apodising filters per se, but rather a function of the specific filter parameters chosen. Peter Craven, when he originally proposed minimum phase filters, also proposed that the filter should roll off very steeply after 20 khz, more steeply even than the usual filters applied at the A/D and D/A conversion. That way, any ringing from the A/D conversion process would be filtered out, albeit at the expense of considerable post-ringing and phase shift from the apodising filter itself - which shows up in JA's measurements.

By contrast, the Ayre white paper I've mentioned frequently before claims that their implementation sounds better with quite gentle filter slopes, which will obviously allow more ringing from A/D conversion to get through, as well as more aliasing distortion, but will create much less post-ringing from the minimum phase filter. That's a pretty interesting disagreement between the ears of two of the best digital audio designers in the business, and JA's evaluation of the new Ayre MP filter will bear watching.

BTW, you must upsample to do apodising, or any digital anti-aliasing filtering, because the filter knee is so close to the Nyquist frequency. Whether you speak of the filtering being applied after upsampling, or as part of the upsampling process, is really a matter of semantics. From the perspective of upsampling the original digital signal, you must upsample in order to filter, and you must filter if you upsample.

Hmm. I seem to recall Bob Stuart mentioning "more gentle" rolloffs. I guess this is why the choice of algorithm came down to listening tests in the end; human psychoacoustics is simply too complex and too poorly understood to do more than generate technical "options" for aural evaluation.

If you've ever listened to that interview/lecture Stuart did for the UK AES, that's almost word for word what he said. Thankfully, there are engineers like Stuart who are willing to trust their ears over their instruments.

VK. Were you awake at the time ?

Must have been if my recollection was spot on!

@scott: I was at the lecture!