Meridian Unplugged - Powered by MrTechGuy.co.uk Forums Discussion Meridian - Systems Apodizing filters already obsolete?

The Ayre white paper is a very simple explanation of these new filter types.

Interestingly, the optimum Ayre MP filter, at least in the published graphs, does not show a steep rolloff at the Nyquist frequency. They claim that a slow rolloff sounds better. But according to both Ayre and Bob Stuart, one of the advantages of the steep rolloff is that it filters out any ringing from the recording or production process. So maybe there's a dispute about what really sounds better, or maybe M has found a way to have their cake and eat it, too.

One more subtlety I note: Ayre says that post-ringing is less audible because it's more analogous to natural sound, and I'm sure that's partly true, but in Bob Stuart's AES presentation, he says that the audibility is reduced due to the ear's "masking" effect, i.e., the ear is briefly deaf to lower level sounds following a louder transient. Masking would obviously not occur for pre-ringing, at least not in our current universe with its forward arrow of time

Bob's description is technically accurate.

I don't think that Ayre's is.

Best,

What part of Ayre's description don't you think is technically accurate?

Ayre's statement seems to me to be just a simplified description of Bob's masking effect.

What Ayre appears to be saying is that almost all naturally occurring sounds have "post-ringing" - think of a guitar string, drum head, etc, etc - so when the ear hears post-ringing from a digital filter, it sounds "natural". Bob Stuart was saying that the ear doesn't hear the post-ringing, because it falls in the temporal masking "shadow" that the ear casts when it encounters a transient sound. As I said in my post above, it's a subtle point, but it seems to me one that speaks to Stuart's formal training in psychoacoustics.

GGA:

scott beat me to it.

I'm unable to distinguish between the filtering philosophies Meridian has been using and Ayre is starting to use with the MP.

I've read through Ayre's white paper and numerous posts to understand the technical aspects, but what does each filtering philosophy mean to the listener?

The reason for my question is I am replacing my Audio Aero Prima MK II and the Meridian G08.2 and Ayre cx-7xe MP are at the top of my list.

Thanks,
Mark

My feeling is that apodizing and minimal phase filters are general techniques. I think Jerry hit the nail on the head when he mentioned that new techniques have tradeoffs, and at this level you are putting your trust on who knows how to make those tradeoffs best.

Lotus and Ferrari both often put their engines in the middle because of weight distribution and polar moment of inertia - all well understood principles, but you'll see the difference between Enzo and Colin in how they handle the subtleties.

Trust your ears; I'd love to hear an unbiased opinion of somebody comparing both. It might be interesting to run both transports through a common DAC to compare just the filters, and skip the analogue. (More apt for processor owners).

I'll take the Enzo!

Hello All,

I'm new here and don't know the forum etiquette. If I break any rules, please let me know kindly, and I will be glad to comply.

In Peter Craven's 2004 AES paper where he coined the term "apodising filter", he defined it as a filter that had a stop-band frequency low enough to eliminate the ringing (pre- and post-) from *any* filters upstream in the entire record/playback chain.

Of course with the CD standard, a filter that eliminates ringing at 22.05 kHz and yet is flat to 20 kHz is going to be a steep son-of-a-gun, which will introduce a lot of ringing itself. Craven's solution to this was to use a *minimum phase* filter instead of the usual *linear phase* filer.

An MP filter works just like an analog filter -- there cannot be any output before the input. So all of the ringing happens *after* the transient event.

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Reducing the values of the taps at the edge of a digital filter is actually called "windowing". There are dozens of windowing functions, such as Blackman-Harris, Gaussian, Kaiser, Hamming, et cetera.

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Hope this helps,
Charles

Welcome to the forum. A competitor not afraid to make themselves public. Good on you.

Are you coming to HH2 event Charles

Just to clarify, *both* of the filters in the demo were MP (minimum phase). The apodizing filter had a steep rolloff so that it was dead flat to over 19.7 kHz and yet had over -100 dB of stopband rejection at 22.05 kHz (where all of the ringing occurs in the "upstream" filters in the record/playback chain). The apodizing filter was *extremely* close to the filter in the Meridian 808.2. I know this because the review of the Meridian in Hi-Fi News last year showed the impulse response of the filter (which basically describes all of the attributes of the filter).

Both our apodizing filter and the Meridian filter (as measured by Paul Miller in Hi-Fi News) have roughly 20 cycles of post ringing. The filter used in the comparison test was also an MP filter, but a much gentler filter with a couple of dB loss at 20 kHz and less good rejection of aliases. (In the time domain, this means that there will be some very small degree of "stair steps" visible on a very high frequency sine wave, for example.)

The Stereophile writers in the room preferred the sound of the slow-rolloff MP filter compared to the sharp-rollof MP filter, as do we at the factory. So we have labeled the slow-rolloff as the "Listen" filter and the sharp-rolloff as the "Measure" filter.

I am glad to answer any other questions.

I'm sorry, I don't know what the "HH2 event" is. In any case, it is very unlikely. I was in a bad accident a few years ago that left me paralyzed. I haven't traveled any further than Denver since then.

However, we do send company representatives to most of the major shows, and I am glad to answer any questions here.

Charles