Noise, Resolution & Benchmark Page 2

Isn't that a problem for the design goals of an amplifier like the Benchmark AHB2? Can such excellent noise and distortion performance be realized in the real world, including my Manhattan apartment? I'll have more to say about noise and distortion later. For now, let's just listen.

A Distortion of Love
In reviewing the Benchmark AHB2, Kal Rubinson played Gerald Finzi's song "Come away, death" (the text is from Shakespeare's Twelfth Night), from the album of that title by mezzo-soprano Marianne Beate Kielland and pianist Sergej Osadchuk. I own that recording, too, in several versions. I played the 24-bit/192kHz version, same as Kal. "Come away, death" is a great piece of music beautifully performed, but it was the "Lullaby" from Mussorgsky's song cycle Songs and Dances of Death (Pesni i Pljaski Smerti) that was more revealing. "Lullaby" has many quiet, breathy moments with quiet, subtle sibilants and fricatives. Those sounds sounded different through the Benchmark system, with more roughness, texture, and complexity. Through my reference system there wasn't really anything to miss—the same moments and sounds were suitably quiet, breathy, and fricative—but through the Benchmark amps those quiet sounds were richer and more interesting. There seemed to be more going on in those quiet moments. It's harder to describe than it was to hear.

Another example: The first note of Changes by Rolf Wallin, from another 2L recording, Symphonies of Wind Instruments, with the Royal Norwegian Navy Band conducted by Ingar Bergby (24/192 download, 2L-102). As a former trumpet player, I've always loved the sonorities of wind ensembles. This piece starts with a literal bang, a loud bass-drum stroke synchronized with remarkable precision with wind instruments and a descending tone from some instrument I don't recognize. It's a loud, abrupt departure from silence. Through the AHB2, it was rougher. There simply was more going on.

1115bench.promo_.jpg

This must be what Kal was writing about when, in his AHB2 review, he reported hearing "much more apparent low-level detail in already-familiar recordings" through the Benchmark amplifiers—though he emphasized the qualifier apparent. What I heard with Benchmark's low-noise system wasn't as dramatic as what he reported, but it was real enough and repeatable: Over the course of several days, I went back and forth between the Benchmark amplifiers and heard it every time. The difference didn't go away.

Were the differences I heard musically important? I'd say no—not in the cases I heard—but they could be important in the right music. While subtle, the differences were as large as or larger than many other details reviewers often emphasize.

Tradeoffs? Kal reported that "Come away, death" and other tracks seemed tonally lighter through the AHB2s than through his usual amplifiers; to him, Kielland, a mezzo, sounded more like a soprano through the Benchmarks. I didn't hear that. In fact, if anything, I thought the AHB2s sounded slightly darker—on certain low notes, Kielland's voice was shifted toward the alto side. Kal was correct when he wrote, "Tonal balance is a curious audio parameter"; it may be the most fundamental parameter in audio, yet how we experience it seems, even more than other aspects of music, dramatically influenced by a range of subjective factors. We could also be hearing the amplifiers' output stages interacting with the loudspeaker impedance to an unusually large extent, though that would surprise me, given the AHB's low source impedance. (JA measured 0.09 ohm at 20Hz and 1kHz including cables, rising slightly to 0.22 ohm at 20kHz.) The AHB2 is a chameleon.

Summing up
Earlier in this Follow-Up, I spent several paragraphs establishing that, even at fairly high listening levels, the quieter parts of the music are below my room's noise floor. How, then, am I able to hear such differences in the music's quieter parts? I gave it some thought and asked some experts, including Benchmark's John Siau.

Noise isn't uniform. Most of the noise in my room is below 120Hz or so, where the ear is quite insensitive. On good, low-noise days, that low-frequency noise is measurably below the threshold of audibility, despite its relatively high level. In the midrange up into the treble, the noise is much lower in level in my room than it is in the bass—but it matters more, because the ear is much more sensitive in that range.

But midrange and treble sounds are directional, so it's easier to distinguish among various noise sources—noise from the speakers vs noise through the windows or from my refrigerator—and to separate room noise from music. As I listened hard to Kielland sing Mussorgsky's "Lullaby" for the third or fourth time, I was aware of noise from my street-side window, but my brain differentiated that noise from the quiet music. It was automatic. I wouldn't say the street noise didn't matter at all, but it mattered less than its volume would suggest.

"Our ears are capable of hearing individual tones that are well below the ambient noise level," Siau told me. "The extreme case occurs at 3kHz, where our ears are most sensitive. At 3kHz, our ears can detect a tone that is 30dB lower than a white ambient noise level, such as the noise created by TPDF dither." (See sidebar.) "In a typical room, the noise is not spectrally flat (white), and it is possible to do much better than 30dB lower than the ambient room noise."

After weeks of obsessing about noise, I'm convinced by another thing Siau told me: If you can't hear noise coming from your speakers while sitting in your listening chair with the source at idle, you haven't got a noise problem. If you can hear noise, that noise is likely to get in the way of the music at times, though it may not matter very much. At a volume setting corresponding to a reasonable listening level, I can't hear any noise coming from my speakers with any of these amps. The low-noise character of the AHB2s, then, apparently isn't important in my room.

But I'm hearing something—a difference—that's correlated with the music: the presence or absence of some sort of distortion or music-modulated noise. Are the AHB2s more "resolving" than my reference? Although I preferred the AHB2s' denser presentation of certain details, it's not clear to me which is truer to the source. Are the AHB2s simply more resolving? Apparently, that's unlikely. (See Siau's comments on resolution in the sidebar.)

Maybe the most important thing a review can do is provide context and a sense of proportion. I’m impressed by the Benchmark AHB2s, but I’m not inclined to buy them—I’m already well equipped. But if you're shopping, try them. It's great that the audio industry offers so wide a variety of equipment with a range of virtues at different price points. My PS Audio BHK 300 monoblocks are capable of great delicacy, but their character is clean and authoritative, and they have lots of power for speakers that present difficult loads. The Pass Laboratories XA60.8 monoblocks, which I also have on hand, emphasize sweetness, richness, and delicacy without sacrificing authority. The less-expensive AHB2s can play in this league and offer a different, and in some ways better, listening experience. It's a fine situation we find ourselves in.

COMMENTS
rt66indierock's picture

With my first office system I had no noise at idle but substitute the Klipsch Hersey's from my home system and I could hear noise at idle.

My office is pretty quiet. Currently 36 to 39 dB with a "river" running underneath it. Without the river at night 24 to 28 dB.

Last year an acquaintance brought his Brenchmark DAC and Amp in with Joseph Audio Pulsars. We noticed and then measured a small difference in the dynamic range of his system and mine. So good job.

John, I'll take "Down in Hollywood" exactly as the 3M machine recorded it. See you Friday.

JimAustin's picture

I'm very curious about your river. I've thought about it and can't figure it out--unless you live on the Pacific coast and over a sea cave. Or something.

rt66indierock's picture

The Phoenix Mountains Preserve is less than two miles away and when it rains like it has the last 72 hours (3.43 inches) a large amount of water flows down the mountains to the flood control canal creating a river.

This river runs under my office into to the flood control canal next to it. I was curious how much extra noise it created so I measured it. Actually not much extra noise.

Nothing left of the river today but it is a regular part of our monsoon season.

Bogolu Haranath's picture

"A River runs Through it" .............. Mark Isham :-) ...........

ok's picture

..but I wonder whether the same or similar listening remarks (since we’re not talking highly differential observations here) wouldn’t have also been possible by using various random configurations for whatever reasons unrelated to real bit depth or THD+N. In my opinion any kind of electronic THD under 0,1% or so is musically meaningless at best (especially when achieved by means of excessive negative feedback which is related to other forms of distortion) mainly due to speaker's erratic frequency response and harmonic distortion bottleneck; pretty much like trying to bypass nearsightedness by increasing screen contrast. However higher figures of electronic THD could arguably accumulate to or even compete certain speaker distortion patterns with rather unpredictable results.

JimAustin's picture

..but I wonder whether the same or similar listening remarks (since we’re not talking highly differential observations here) wouldn’t have also been possible by using various random configurations for whatever reasons unrelated to real bit depth or THD+N.

Yes, that is possible. It would be exceedingly time-consuming to rule out that possibility.

In my opinion any kind of electronic THD under 0,1% or so is musically meaningless at best (especially when achieved by means of excessive negative feedback which is related to other forms of distortion) mainly due to speaker's erratic frequency response and harmonic distortion bottleneck; pretty much like trying to bypass nearsightedness by increasing screen contrast. However higher figures of electronic THD could arguably accumulate to or even compete certain speaker distortion patterns with rather unpredictable results.

I was, frankly, surprised to hear a difference. And while it was obvious once identified, it's not something you'd notice in casual listening--regardless of whether or not it correlates with THD+N. This is very close to what I set out to test--though, as my answer to your first question acknowledges, the test is more suggestive than definitive. Maybe the obvious conclusion from this experiment is that the kind of numbers Benchmark has achieved are most useful in the studio--and especially at the conversion stage, where there may be several conversions. In a studio, a power amplifier is used for monitoring only--so, a single pass. The AHD-2 is a great amplifier, but unless the differences I heard are indeed attributable to distortion and noise, I don't know why anyone, even a studio, would need an amplifier that clean.

JimAustin's picture

I thought I should add, having just rewritten what I wrote a few weeks ago: I'm convinced that noise is not responsible for the differences I heard. I'm convinced that, as I wrote, if you can't hear noise, noise is not a problem; after all, you can hear through noise. I'm far less convinced about distortion. Distortion, correlated with the music, can obscure detail. At what level, I'm not sure.

ok's picture

..I've also heard this amp; it sounded truly remarkable – and I don't mean merely on the detail department.

Ortofan's picture

... "excessive" negative feedback:
https://linearaudio.net/sites/linearaudio.net/files/volume1bp.pdf

ok's picture

of Bruno’s views on a handful of matters and as far as I know he’s not a proponent of feedback excess in non-class D amplifiers. In this very paper (p. 14-15) he clearly states that his use of excessive NF in conventional amps is purely experimental and mostly unstable, while “normal” amounts of global feedback admittedly render their sound somewhat unpleasant (well, not that I'd personaly reject any amp merely on feedback grounds). By the way his class D amps and active speakers tend to sound arguably better than some 90% of the current hi-end circulation.

Bogolu Haranath's picture

Manufacturers of conventional SS amps like Ayre and Pass use almost no NF ........... Two examples ........

dalethorn's picture

When it comes to power amps, I think it's foolish to skimp on anything. If it doesn'r weigh at least 300 lbs and raise the room temperature noticeably, it's too weak.

Ortofan's picture

... negative feedback (as it applies to electronic circuits), perhaps you can quantify the amount of negative feedback that you deem to be "excessive" and describe how you make that determination?

ok's picture

should be considered within context, not per se. Compromises usually need to be made between low THD+N, wide bandwidth, high damping factor pros and gain drain, higher order distortion pattern, brick wall clipping etc cons. Class D amplifiers may need more than 30 db of global feedback to effectively operate, while some class A/B ss or tube designs are doing all right with just 3 db bordering to none. There are also power amplifiers (CH Precision comes to mind) that allow the end user to swap between global and local feedback depending on speaker impedance and personal taste. Your question, if not teasing, otherwise reminds me of the ancient greek “sorites paradox” which seeks to determine the exact point where accumulated grains of sand actually become a heap.

Bogolu Haranath's picture

Some tube amp manufacturers provide user adjustable feedback controls .......... Cary Audio is one example ............

Ortofan's picture

... amplifier. How do you determine whether or not a given amp employs what you refer to as an "excessive" amount of negative feedback?

ok's picture

..THD and damping factor; if it works, I don't mind.

Ortofan's picture

... do you want an amp to have?

ok's picture

..above 20 something is actually marketing overkill. When cable/crossover/voice coil is taken into account, there is no such thing as a DF of 1000. I've heard zero-feedback amp with a measured DF of 18 that handled bass with Darth Vader force grip; same figure in a feedback-based amplifier would arguably suggest an embarrassing piece of junkware.

Ortofan's picture

... that audible variations in frequency response won't be introduced when such an amp is used with a speaker having a non-linear impedance?

ok's picture

and even measurable to a certain degree, though it actually depends on many a factor (output devices, power supply, bias current, signal path etc) amongst which nominal output impedance is probably the least significant one. In general I find speaker measurements (please someone add distortion figures!) far more straightforward and informative than the electronics counterpart, the actual meaning of which remains in many a case rather obscure. Or, as Putzeys puts it (referring to MQA): “Meanwhile I'm happy to do speakers. You wouldn't believe how much impact speakers have on replay fidelity”.

Bogolu Haranath's picture

Putzeys designed Kii Audio Three loudspeakers using his Class-D internal amplifiers ........ The speakers are listed under Class-A Stereophile ............

Bogolu Haranath's picture

Nelson Pass talks about amplifier design in an article published by Stereophile .......... That article can be found at Stereophile References ..........

Ortofan's picture

... are you then willing to accept as a by-product of using an amplifier with a relatively lower damping factor (or higher output impedance)?

ok's picture

since I already own a decade old, modestly powered, zero feedback integrated combined with some 88db/m, mostly 4 to 3 ohms, almost flat 35Hz-20KHz response (all according to third party actual measurements) 3-way floorstanders and I can attest that the results are nothing less than extraordinary from whisper to shout for any casual city dweller. Cables are of crucial importance but nothing really extravagant. Never mind names and prices – not to be found at Recommended Components either.

Ortofan's picture

... the fabled mystery amp and speakers.

Their performance is always described as "extraordinary" when the make and model of the equipment somehow can't be revealed.

ok's picture

..but it was just an interview, not an advertisement as your average posts.

Ortofan's picture

... the Socratic method won't succeed.

ok's picture

..the aforementioned speakers are favorably presented in JVS’s latest RMAF report driven by some tube integrated. Measurements are easily accessible through the net I suppose ;-)

jeffhenning's picture

So the amp with the greatest linearity, least noise and least distortion might not be the most resolving, truest amplifier?

Sorry, but that seems nonsensical. Are you sure your speakers are really up to the task? Sorry again, I don't think they are.

I'll closely paraphrase Benchmark's John Siau in what he wrote me 3 years ago (my memory is not photographic): "When you first hear an amp like the AHB2 if you are used to amps with more noise and distortion, the AHB2 may sound wrong. Given some time, that fades. In the end, the superior amp will sound always better."

JimAustin's picture

Can't help thinking you didn't read the article, or not carefully.

Bogolu Haranath's picture

HR wrote an interesting article about loudspeakers, which was recently published on the AudioStream website ....... Interesting article and interesting comments :-) ..........

Solarophile's picture

So what did HR say that was of any relevance here? As usual, I found his thoughts rather vague in that article.

Bogolu Haranath's picture

May be the loudspeakers are the weak link? :-) .............

Solarophile's picture

Speakers and headphones are always the weakest link compared to any decent DAC or amplifier whenever we start comparing things like distortion.

Robin Landseadel's picture

No LP playback will ever have s/n ratios like these. Kinda hard to think of LP reproduction being "high resolution" in this context.

Bogolu Haranath's picture

The SNR of vinyl LP is approx. 50-55 db ........... which is approx. 8-10 bits .........

Bogolu Haranath's picture

The SNR of analog reel to reel tape is approx. 72 db, which is approx. 12 bits ...........

Bogolu Haranath's picture

The SNR of analog cassette tape is approx. 63 db, which is approx. 10 bits .........

Bogolu Haranath's picture

The SNR of DAT is approximately the same as CD .............

Bogolu Haranath's picture

Nagra makes a digital reel to reel audio tape machine (the company says is) capable of recording in 24/96 resolution ..........

Bogolu Haranath's picture

JA recorded "Duet" album with a Nagra-D digital tape recorder at 24/88.2 resolution using "Decca Tree" 3 microphone configuration ..........

dalethorn's picture

I'm still waiting on a definitive list of "Decca Tree" recordings, with all of the facts in one list. I'm so busy arresting immigrants these days that I don't have time to build my own list from scratch.

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