[music_man]

Quote:

Originally Posted by s.a.b. /img/forum/go_quote.gif I have the DAC1 and k701 (as well as DT880 ('03) and DT990) and I wouldn't describe the reality as "brutal" at all.

what do you mean by that statement? i didn't mean that the dac1 is "brutal". i meant to say that most people don't want to know how poor their recordings(in my case cd's) are.

most audiophiles don't want the "truth". even though they say they do. ie, the truth being the recording as it exists with nothing added or subtracted. or as little as possible. most audiophiles want a pretty rendition of the truth pertaining to their particular tastes. regardless of what most audiophiles will admit.

i admit it is tough to hear the blatant reality of most poor recordings. those that are supurb are tough to listen too for other reasons. they demand utmost attention of the listener or they become fatiguing. the dac1 provides this type of exacting performance.

music_man

 

[yourmando]

Quote:

Originally Posted by Jetlag /img/forum/go_quote.gif I am certainly not a paid Benchmark shill, but every technical review I have read about the DAC1 has essentially echoed the same thing that Elias mentioned in his earlier post. That is; this device converts digital audio to analog audio in the most precise and accurate way possible while completely blocking jitter and it's potential negative effects on this process. This is precisely what I want from a DAC (or really any audio gear for that matter).

Quote:

Originally Posted by Crowbar /img/forum/go_quote.gif There are always ways to improve quality given any equipment, such as using multiple DACs and dithering the LSBs, as modern DAC chips are not accurate to the full 24 bits (an examle of this is the Anagram module which several high end DACs use). But of course, such things increase the price. Another thing is that most solid state amplifiers have thermal memory distortion which doesn't affect THD and IMD measures. See this AES paper: http://www.aes.org/e-lib/browse.cfm?elib=7497 It's not new discovery; it's been known for long before by designers of vertical amplifiers in oscilloscopes. In the tube world, it exists but the time constant is far larger and below the audio band; it only affects DC there. It is worst in chip amplifiers such as op amps, where the input stages are thermally coupled to the output stages. ... Asynchronous resampling attenuates jitter and embeds it in the data; it does not remove it. ... Well, you got one out of three points correctly, so that's not too shabby ;P

You might be surprised to learn that the Benchmark DAC1 is actually entirely immune to jitter under all operating conditions. Their UltraLock design includes much more than an Asynchronous Sample Rate Converter to attenuate jitter. Check out the graphs in the manual:

http://www.benchmarkmedia.com/manual...USB_Manual.pdf

We can see total jitter immunity to the limits of the Audio Precision System 2 Cascade test unit, up to 12.75 UI (2075 ns) of jitter. There is also a graph showing complete immunity to cable induced jitter by comparing a run of the mill 1000' (~305 m) unshielded cat 5e data cable to a direct digital input--no jitter induced sidebands. Another graph shows the eye pattern of multiple 1000' data cables and even the one with the tiny eye pattern sees no change in performance.

As for improving the quality of the conversion--I have not seen any measured results that are as good as the dac1 under as wide a range of operating conditions. (Rant: often, only a few specs are provided, sometimes without stating measurement conditions, and it seems that some manufacturers simply list the specs of the dac chip they use, or misleading specs such as SNR that includes the output mute circuit.)

In terms of measurable accuracy, the DAC1 is up there with any dac at any price, and performs as specified independent of sampling frequency, jitter, for very long digital and analog cable runs, through the full usable level range. And most importantly to us, the headphone outputs deliver the full rated performance of the dac1 (performance just as good balanced and unbalanced outputs), even at very high levels, and for headphones loads from 30 ohm to 600 ohm with no change in performance.

I would personally give Jetlag a 3 out of 3 in his assessment! That's not to say we won't ever see effective number of bits approach 24 if we move past current technology. Given the alternatives, and that we are really limited by the best A/D converter used for the very best source material, and that we are probably already well past the audibility threshold for something at this stage in audio reproduction signal path, I would say we have hit the state of the art!

Armando

 

[music_man]

i'd like to hear comments from people that are impressed with the headphone outputs and what level of stand alone amps they would compare it to.

i am wondering if i should add an outboard amp to it and what is likely to considerably exceed the built in amps with k701's. if anything. i am very impressed with the accuracy and transparency of the dac1 both as a dac and headphone amp. i'd like to stick with that. i do not want to add an amp to it that has it's own sound.

music_man

 

[Lord Chaos]

Music Man, I'm no expert on headphone amps but I have been using them since the days of the Shure Solo-Phone. I've also spent a lot of time recording. So, I can't say the HPA2 is the world's best headphone amp, but I can say it's the best sounding component I've ever heard. I look forward to putting on the headphones and disappearing into the music, which is what happens with a good recording.

I think that anyone looking for high-quality sound would be pleased with the DAC1 and its headphone amp. I bought mine simply because it provided everything I needed in one box, and the reviews I read were positive. I bet $1000 that I'd like it too, and I do. So, I bought another one to use at my desk.

 

[Crowbar]

Quote:

Originally Posted by yourmando /img/forum/go_quote.gif We can see total jitter immunity to the limits of the Audio Precision System 2 Cascade test unit, up to 12.75 UI (2075 ns) of jitter.

I find it strange that the highest jitter frequency tested was 9 kHz, when jitter effects increase with frequency and is very significant even above 20 kHz. Take a look at this article by Lavry: http://www.lavryengineering.com/white_papers/jitter.pdf
Of course, the nature of the effects going through an ASRC would be different, but is no reason not to consider such test cases.

I'm also interested in the level of jitter after the ASRC, which is mostly dependent on the local clock. Dunn's paper from the 93rd AES convention derives a 20 ps maximum allowable: http://www.nanophon.com/audio/jitter92.pdf

Quote:

As for improving the quality of the conversion

What do you mean? No current DAC chip manages actual 24 bits resolution; about 21 is the highest I've seen. More can be done with multiple DAC chips and scrambling. If you mean the quality of the IV conversion, I suggest you check out Hawksford's current-steering transimpedance amplifiers paper. In simulation, Fig.4-4 is the best performing IV I've seen, and from those that have built it I've not seen anything to make me doubt those results. Of course, tuning a discrete design where parts must be matched may not be economic for certain price ranges.

Finally, you quoted me mentioning the thermal memory distortion, yet you did not address that point. This issue is most significant with chip amps (as even a skeptic like D.Self will point out), which is another reason to prefer discrete designs. This doesn't really show up in THD measurements. It would be interesting if someone would perform the memory measurement described in the paper I quoted before on various SS stages, including this one.

Quote:

(Rant: often, only a few specs are provided, sometimes without stating measurement conditions, and it seems that some manufacturers simply list the specs of the dac chip they use, or misleading specs such as SNR that includes the output mute circuit.)

That is unfortunately the case. Summary metrics like THD/IMD have limited utility as they're not perceptually weighted. Some distortions are inaudible to a couple of percent (i.e. low order even harmonics), others in the parts per million (B/AB class crossover distortion). Some have audibility established but the ear's exact sensitivity to them not determined (such as the thermal memory issue I mentioned above).

Quote:

In terms of measurable accuracy, the DAC1 is up there with any dac at any price

I've mentioned some measurements that I don't see there. I'm not singling out the DAC1, I'm talking about DACs in general, and I'm glad the DAC1 at least shows the amount of detailed measurements that it does; hopefully it will set a trend. But I would not say they are sufficient to justify your claim.

Quote:

and that we are really limited by the best A/D converter

As I pointed out above, we are not. You can use a bunch of them to get an improvement.

Quote:

we are probably already well past the audibility threshold for something at this stage in audio reproduction signal path

That's an unwarranted statement. The ITU recommends double-blind triple-stimulus with hidden reference testing; I'll believe it when I see the results.

There are many other things wrong with sound reproduction besides the electronics, such as that all speakers and headphones have tremendous distortion (well, with the exception of Alan Hill's helium plasma device in the 1 kHz and up range). Even worse is the recording and playback geometry. Several things like binaural, Ambisonics, etc., but none of them work very well. The single thing that will make most of an improvement in audio is having one's personal HRTF. It's already well established that HRTF differences between individuals are very significant. I find it quite amusing when I read reviews about how some amp makes the imaging clearer and such nonsense, when it has nothing to do with that. HRTF measurement needs an anechoic chamber and expensive equipment, but in recent years the alternative of laser scanning and finite boundary method simulation allows one to compute the HRTF. I wonder how long until hi-end audio stores start carrying laser scanners so one can just go and get a scan, then they compute the HRTF, for a fee, and you can use it in your favorite DSP convolver to make those binaural recordings made with the pinna-less dummy head really give the right positional sound. Anyway... getting too offtopic here with my rant

 

[EliasGwinn]

Quote:

Originally Posted by s.a.b. /img/forum/go_quote.gif I have the DAC1 and k701 (as well as DT880 ('03) and DT990) and I wouldn't describe the reality as "brutal" at all. I do have the ago old questions for Elias - at least when listening thru headphones, I (and even non-audiophile folks at my house) do hear a difference between transports and even digital cables. Any thoughts on this? Thanks.

s.a.b.,

I'm not sure what is causing the differences you are hearing, but we have done extensive testing with different types of digital cables, and we have not been able to hear or measure any differences using various cables with the DAC1. Different analog cables can affect the output sound of the DAC1, but we have not been able to find any performance differences with different digital cables.

As Crowbar mentioned, sometimes its really difficult to hear differences between set-ups without a proper testing configuration. When conducting an A/B test, its very easy for even the most trained ear to lose their point of reference, making it very difficult to make accurate comparisons.

Thanks,
Elias

 

[StevieDvd]

Elias,

Thanks for the continued updates and persevering with the multiple and sometimes extensive questioning.

Can I just ask for suggestions/tips on using the DAC1 balanced xlr outs feeding into a balanced headphone amp? Any optimum or suggested settings?

Embarrasses me to admit I just left it at factory settings, all sounds well but it's be nice to know I'm not missing out for the sake of flipping a switch or jumper around.

My amp (Rudistor NX-33) volume control goes to about the 12 o'clock position before it gets too loud to use.

I read your position on using balanced headphones directly from the Dac1 but that's what I did initially before upgrading to balanced amp.

Have you opinions on balanced amps too?

Steve

 

[The Monkey]

Elias,

One design note for the good folks at Benchmark. The screws that need to be undone in order to get inside the unit could be improved. First, mine were screwed in so tight that it was almost impossible to remove them. Second, it is very easy to damage or "strip" the screw heads themselves. I'd love to see Benchmark go with hex socket head screws or thumb screws.

 

[EliasGwinn]

Steve,

The factory settings on the DAC1 are suited to fit most set-ups. How far are you turning the volume pot of the DAC1? If you are not able to get the volume knob past 10 o'clock or so, then you may want to change the output attenuators.

As for running balanced into an amp, that is the best way to interconnect the DAC1 and another device. Balanced headphones are a whole other subject...

On the subject of balanced headphones, we have found no evidence, documentation, or explanation to support the claims of performance advantages. For those familiar with bridged-mode power amplifiers, balanced headphones are a very similar topology....

Bridged-mode amplifying is used to increase power into a given load, while sacrificing performance (especially damping factor). This mode of operation is undesirable unless an increase in power is absolutely necessary.

From everything we have seen, balanced headphones suffer from the same symptoms, while not having any benefits to offer. The benefit of bridged-amping (additional power) is not needed in this case (the DAC1's headphone output has more then enough power for any headphones we have encountered). Therefore, we simply have no reason to believe there are any advantages.

Some people may enjoy this particular configuration, and we encourage those people to continue to enjoy it.

As a company and equipment designer, we choose to follow routes of technology which are founded in some sort of explainable / provable / understandable manner. Otherwise, we would be chasing every whim and trend that floated through the audiophile community (and, trust me, that could get very exhaustive

).

Thanks,
Elias

 

[EliasGwinn]

Quote:

Originally Posted by The Monkey /img/forum/go_quote.gif Elias, One design note for the good folks at Benchmark. The screws that need to be undone in order to get inside the unit could be improved. First, mine were screwed in so tight that it was almost impossible to remove them. Second, it is very easy to damage or "strip" the screw heads themselves. I'd love to see Benchmark go with hex socket head screws or thumb screws.

Monkey,

Thank you very much for this very valuable feedback. I will bring this up with our production team.

Thanks,
Elias

 

[music_man]

mr gwinn,

is the dac circuit connected to the headphone amp circuit balanced on the pcb? if not, why and how is it connected? edit: it appears that it is unbalanced?

also, what is the headphone amp using in place of an op-amp as the amplifier? a buffer ic? edit: wasn't it discussed that the headphone amp was discrete? there is mention of op-amps here.

edit: is there a pot on the pcb to adjust the headphone amps gain?

thanks,
music_man

 

[yourmando]

Quote:

Originally Posted by Crowbar /img/forum/go_quote.gif What do you mean? No current DAC chip manages actual 24 bits resolution; about 21 is the highest I've seen...

I didn't mean to quibble with any specific points, but thought you might be interested to know that the DAC1 jitter immunity is more than just attenuation from an ASRC. Yes, I did mention that the effective number of bits of any DAC has not hit 24 bits (And this is probably not possible with current technology because of the thermal noise floor at room temp). My original point is that the DAC1 represents the current state of the art in terms of measurable performance over a wide range of real world operating conditions.

For a third party look with Audio Precision measurements of the non-usb DAC1:
http://theaudiocritic.com/blog/index...Id=10&blogId=1

I can't say it better than that! The USB version has more features (beyond USB) and a wider range of operating conditions.

Armando

 

[Crowbar]

Well, specific points are what makes a discussion concrete, and I wouldn't call it quibbling. Looking at the linearity graph in your link, it's linear to about -115 dB. I don't know what DA chip is used in the DAC1, but AD1955 datasheet shows linearity down to -125 dB, and that's a 5 year old IC. The PCM1794A has similar performance. Both are cheap. My other two points are not discussed at the site you linked to. The dither test is nice, showing the ~18.5 bit effective resolution. Still, I'd still like to see the high frequency jitter test I mentioned above, and especially the thermal memory measurement. I would guess the DAC1 would do fine in the former, but I have my doubts about the latter due to the use of opamps.

 

[yourmando]

Quote:

Originally Posted by Crowbar /img/forum/go_quote.gif That's an unwarranted statement. The ITU recommends double-blind triple-stimulus with hidden reference testing; I'll believe it when I see the results. There are many other things wrong with sound reproduction besides the electronics, such as that all speakers and headphones have tremendous distortion...

I would also love to see more double blind tests! In absence of this, I will pick the product with the best and most extensive measurements (and useful features), even if I feel it is probably overkill. That we are "probably" well past the audibility threshold is a sufficiently hedged comment. I, too, love to learn about the limits of perception, the design gear, etc. Like you, I believe that transducers--loudspeakers and their interaction with the room, headphones--are by far the limiting factor; The speakers are the sole determinant on the reproduction side of the width, height, and depth of the sound stage and size of virtual images (aside from intentional or unintentional distortion/processing in the electronic signal path).

Let me put it this way, if a friend wanted a recommendation on the best near-field audio reproduction electronics components, I would recommend a computer or bit-perfect streamer as the source (not a cd player that I have to feed!), and a Benchmark DAC1 USB as the DAC/preamp/headphone amp with the volume control kept within arms length, because I know of no other combination with this level of end to end distortion and noise with real resistive loads. (This doesn’t include multiple channel and DRM restricted audio, which would require another setup.)

Cheers,
Armando

 

[yourmando]

Quote:

Originally Posted by Crowbar /img/forum/go_quote.gif Well, specific points are what makes a discussion concrete, and I wouldn't call it quibbling. Looking at the linearity graph in your link, it's linear to about -115 dB. I don't know what DA chip is used in the DAC1, but AD1955 datasheet shows linearity down to -125 dB, and that's a 5 year old IC. The PCM1794A has similar performance. Both are cheap. My other two points are not discussed at the site you linked to. The dither test is nice, showing the ~18.5 bit effective resolution. Still, I'd still like to see the high frequency jitter test I mentioned above, and especially the thermal memory measurement. I would guess the DAC1 would do fine in the former, but I have my doubts about the latter due to the use of opamps.

You are certainly the tough critic! “The” Audio Critic, champion of mesurement-driven and DBT evaluation was much “softer” than you:

Quote:

The cloud-cuckoo-land high-end DACs at ten times and fifteen times the Benchmark’s price are no better and in most cases not as good... Why can I confidently make that statement? Because I measured the DAC1 up and down and sideways with the Audio Precision SYS-2722, possibly the most sensitive and accurate audio-test instrument in the world, and found it to be as nearly perfect as a digital-to-analog converter can get at the present state of the art. Totally perfect 24-bit converters, with the theoretical noise floor of –146.24 dBFS and a perfect monotonicity “staircase” waveform at the ten lowest LSBs, do not yet exist, at any price, and probably never will. Still, the DAC1 yielded the best measurement figures that I have ever obtained out of a digital processor on my test bench, nor have I ever seen better measurements on other units in other publications... ...I’ll take electronic perfection, any day of the week, if it costs $975 instead of $17,500.

We have about 20 pages in the DAC1 manual of Audio Precision graphs and specs, seven more independent graphs in the article linked above, and I’m sure there are plenty more out there. Your drive to know more amazes me. Good luck in your search, and please do let me know if you find some more data, or another unit with a comparable set of measurements showing better performance all the way to headphone amp stage with at least the same range of operating conditions!

Armando