You are here

Log in or register to post comments
hollowman
hollowman's picture
Offline
Last seen: 2 months 1 week ago
Joined: May 28 2009 - 12:59pm
Impulse test for Stereophile digital Measurements

The Impulse test shows up in JA's Measurements from time to time. May 2011's HiFiMan 602 included it and may have been significant: the total lack of pre- and post-ringing may be one reason NOS (non-oversampling, aka zero oversampling) has a certain appeal, despite other horrible metrics (and other horrible sonic attributes).

The Meridian 808 review from April 2009 also included the Impulse response test and associated discussion of apodizing (an minimum phase) filters. In that review, JA noted that part of the reason the 808 sonically excelled may have been control of pre-ringing (ala its software-based apodizing filter). Could control of pre-ringing -- via engineered reconstruction or NOS -- be another 'holy grail' of digital-audio evolution? ... i.e., much like the "discovery" of linearity and jitter in the late 80's and early '90s, respectively? Why isn't the impulse test done more regularly in Stereophile digital-gear measurements?

I'm curious as to how formerly-reviewed NOS gear -- like Zanden and 47 Lab -- perform (methinks it will be similar to the HiFiman 602).  Perhaps more importantly, Ayre  and Cambridge Audio (both of whom putatively use MP and/or apodizing reconstruction) did not include (TTBOMK) impulse tests. It would be an interesting correlation experiment!

hollowman
hollowman's picture
Offline
Last seen: 2 months 1 week ago
Joined: May 28 2009 - 12:59pm
Impulse test vs. Impulse test
hollowman wrote:

I'm curious as to how formerly-reviewed NOS gear -- like Zanden and 47 Lab -- perform (methinks it will be similar to the HiFiman 602).  Perhaps more importantly, Ayre  and Cambridge Audio (both of whom putatively use MP and/or apodizing reconstruction) did not include (TTBOMK) impulse tests. It would be an interesting correlation experiment!

I just noticed that JA did perform an impulse test for the Ayre DX-5 review from Dec 2010. Interesting that it looks way better than the Meridian 808.2 from April 2009. Alas ... these units may, in their latest versions, have been upgraded in *so many ways not related to MP/apodizing filters*, that it's hard to truly know why  their SQ *actually* improved.

John Atkinson
John Atkinson's picture
Offline
Last seen: 7 hours 18 min ago
Joined: Nov 7 2010 - 3:31pm
Re: Digital Impulse Responses

hollowman wrote:
Why isn't the impulse test done more regularly in Stereophile digital-gear measurements?

Because in 99.99% of cases, the impulse response is that of a conventional FIR filter, ie, symmetrical in the time domain with as much "ringing" before the peak as after: see the Benchmark DAC1's impulse reponse in fig.1 at http://www.stereophile.com/content/meridian-8082808i2-signature-reference-cd-playerpreamplifier-measurements. I only publish the impulse response when it is _not_ like that. You can infer the impulse response, BTW, from the undithered waveform at -90.31dBFS, which I always publish in my digital reviews. A conventional FIR filter gives symmetrical overshoots to the edges of the squarewave.

Quote:
I'm curious as to how formerly-reviewed NOS gear -- like Zanden and 47 Lab -- perform (methinks it will be similar to the HiFiman 602).

That is correct.

John Atkinson

Editor, Stereophile

hollowman
hollowman's picture
Offline
Last seen: 2 months 1 week ago
Joined: May 28 2009 - 12:59pm
JA, thx for your

JA, thx for your reply. That Meridian post-ring is still awfully ugly. What kind of analog filter are they using with unit (eg, no. of poles, etc.)?

Something else I realized is that newer MP/apodizing filters -- used in Meridian, Ayre, etc. -- may have (in addition to better traditional oversampling) also been written to correct for shortcomings in the A/D part of chain. So NOS's "clean" impulse plot may have v. little, if anything, to do with "NOS sound".

Back to how efficacious MP/apodizing filters are ... well, the Keith Howard-engineered tests from Jan 2006 didn't help the case for these filters! But, maybe, those were old-school MP filters; Meridian/Ayre have been busy since then, so perhaps their math is better??

hollowman
hollowman's picture
Offline
Last seen: 2 months 1 week ago
Joined: May 28 2009 - 12:59pm
Wadia and Theta vs. time-domain reconstruction

Wadia and (I think) Theta putatively addressed time-domain issues quite early on in the reconstruction game. Anyone know how their impulse responses looked? (I went thru most of my 28-year Stereophile magazine stack (uh .. stacks!!) but found nothing.

John Atkinson
John Atkinson's picture
Offline
Last seen: 7 hours 18 min ago
Joined: Nov 7 2010 - 3:31pm
Re: Wadia and Theta vs. time-domain reconstruction

hollowman wrote:

Wadia and (I think) Theta putatively addressed time-domain issues quite early on in the reconstruction game.

Wadia, yes, and Sony and Pioneer, but not Theta.

Quote:
Anyone know how their impulse responses looked? (I went thru most of my 28-year Stereophile magazine stack (uh .. stacks!!) but found nothing.

I just posted the impulse response of the Wadia 850 to the Stereophile magazine Facebook page. It is symmetrical in the time domain with minimal ringing.

John Atkinson


Editor, Stereophile

  • X
    Enter your Stereophile.com username.
    Enter the password that accompanies your username.
    Loading