rob watts said:

I have been seeing some comments describing Hugo as excellent DAC with a good headphone amp. Both comments, in my view, are wrong and way off the mark - and seeing these comments are starting to bug me, so I would like to get it off my chest. So forgive me if I am overstepping the mark - commenting on honest posts about a product I have designed, but I thought it might be useful for Head-fi'rs to read my views.

First, I would like to talk about what as a designer I am trying to accomplish, as it has a bearing on one's opinion of Hugo's sound. Imagine going around CES and carefully listening to all the high end hi-fi on show, so you can carefully listen to all the major high end brands available today. Next, listen center stage row 10 to an orchestra. Now, in my opinion, high end Hi-fi sounds from very bad to absolutely awful compared to live acoustic music. The key difference in the sound is variability - live acoustic music has unbelievable variations in the perception of space, timbre, dynamics and rhythm. Additionally, each instrument sounds separate and as distinct entities. By comparison, high-end audio is severely compressed - depth of sound stage is limited to a few feet (listen to off stage effects in say Mahler first - in a concert the off stage effects sound a couple of hundred feet away but on a hi-fi it is an ambient sound a few feet away). Timbre is compressed - you don't get a really rich and smooth instrument playing at the same time as something bright. The biggest problem is the dominance effect - the loudest instrument is the one that drags your attention away - this constant see-saw of attention is the biggest reason for listening fatigue, a major problem with Hi-fi.

So I am approaching designing of Hi-fi from the POV of accepting that there are enormous differences between conventional Hi-Fi and real music, and that I want my equipment to be as transparent as possible. Now some peoples idea of transparency is to use distortion to artificially enhance the sound, and this is a real problem with listening tests - a superficially brighter sound, giving the impression of better detail resolution, is often distortion. So a real challenge is defining what true transparency is. My definition, is to latch onto the idea of variations - if a modification makes the sound more variable, then its more expressive, and hence more transparent, even if it sounds, in tonal balance, darker or smoother and superficially less impressive. Now, if you think that your Hi-Fi sounds better than live acoustic music - then fine, we will agree to disagree. You are looking for a sculpted sound, not a truly transparent one, and I would strongly advise never to buy equipment designed by myself, as I am striving for equipment with no added sound.

So how does this relate to Hugo? Hugo was on the tail end of a long series of incremental improvements in digital design. I have spent the last 7 years on R and D to fundamentally improve aspects of DAC performance - improvements in the jitter rejection, RF noise filtering, noise shaper topologies, WTA filter length, analogue design plus a lot of other things. Moreover, Hugo took advantage of a big step forward in the capabilities of FPGA's - I could do important things that I knew influenced the sound but that previously were not possible due to FPGA limitations. So Hugo was at the confluence of two events - a big step forward from 7 years work in understanding digital design plus a major step forward in FPGA capability. It is just an accident that it happened with a portable headphone product.

So Hugo was the first instance when all these improvements came together. When I finally heard the pre-production unit with all the improvements in place I could not believe the sound quality improvements that I first heard. It completely changed my expectations of what was possible from digital audio - I was hearing things that I have never heard from Hi-fi ever - in other words, the gap from Hi-fi to live acoustic music was suddenly very much closer. Most notable was rapid rhythms being reproduced with breathtaking clarity - before piano music sounded like a jumble of notes, now I could hear each key being played distinctly. The next major change was timbre variations - suddenly each instrument had their own distinct timbre qualities, and the loudest instrument dominance effect was gone. Also gone was listening fatigue - I can listen for 12 hours quite happily.

But by far the biggest change was not sound quality, but on the musicality. I found myself listening and enjoying much more music, in a way I have never experienced before with a new design (and anybody who knows something of my designing career knows that is a lot of designs). 

So my conclusion is this: Hugo does things that no other DAC at any price point does. Now I can say readers saying, well OK he would say that anyway, it's his baby. True - I can't argue with that POV. But let's examine the facts:

1. The interpolation filter is key to recreating the amplitude and timing of the original recording. We know the ear/brain can resolve 4uS of timing - that is 250 kHz sampling rate. To recreate the original timing and amplitude perfectly, you need infinite tap lengths FIR filters. That is a mathematical certainty. Hugo has the largest tap length by far of any other production DAC available at any price.

2. RF noise has a major influence in sound quality, and digital DAC's create a lot of noise. Hugo has the most efficient digital filtering of any other production DAC - it filters with a 3 stage filter at 2048 FS. The noise shapers run at 104 MHz, some 20 times faster than all other DAC's (excepting my previous designs). What does this mean? RF noise at 1 MHz is 1000 times lower than all other DAC's, so noise floor modulation effects are dramatically reduced, giving a much smoother and more natural sound quality.

3. The lack of DAC RF OP noise means that the analogue section can be made radically simpler as the analogue filter requirements are smaller. Now in analogue terms, making it simpler, with everything else being constant, gives more transparency. You really can hear every solder joint, every passive component, and every active stage. Now Hugo has a single active stage - a very high performance op-amp with a discrete op-stage as a hybrid with a single global feedback path. This arrangement means that you have a single active stage, two resistors and two capacitors in the direct signal path -  and that is it. Note: there is no headphone drive. Normal high performance DAC's have 3 op-amp stages, followed by a separate headphone amp. So to conclude - Hugo's analogue path is not a simple couple of op-amps chucked together, it is fundamentally simpler than all other headphone amp solutions.

This brings me on to my biggest annoyance - the claim that Hugo's amp is merely good. Firstly, no body can possibly know how good the headphone amp in Hugo is, because there is not a separate headphone stage as such - its integrated into the DAC function directly. You can't remove the sound of the headphone amp from the sound of the DAC, it's one and the same.

Struck by these reports, I decided to investigate, as I see reported problems as a way of improving things in the future. I want to find weakness, my desire is to improve. So I tried loading the OP whilst listening on line level (set to 3v RMS). With 300 ohm, you can hear absolutely no change in sound. Running with 33 ohm, you can hear a small degradation - its slightly brighter. This is consistent with THD going from 0.0004% to 0.0007%. Note these distortion figures are way smaller than desktop headphone amps. Also note that with real headphones at this level you would be at typically ear deafening 115dB SPL. Plugging in real headphones (at much lower levels) gives no change in sound quality too. This has been reported by other posters - adding multiple headphones to Hugo does not degrade sound at all.

So how do we reconcile reports that desktop headphone amps sound better? I don't believe they do, its a case of altering the sound to suit somebody's taste. Now as I said at the beginning of this post, that is not what I want to do - I want things to sound transparent, so that we can get closer to the sound of live acoustic music. Adding an extra headphone amp will only make things worse as extra components degrades transparency. Another possibility is that people are responding against Hugo's unusually (for a headphone amp) low output impedance of 0.075 ohms. Now, compared to headphone amps of 2 to 33 ohms impedance, this will make the sound much leaner with less bass. Additionally, the improvements in damping can be heard as a much tighter bass with a faster tempo. So if you find your headphone too lean, the problem is not Hugo's drive - your headphone is just been driven correctly.                 

Just to close to all Hugo owners - enjoy! I hope you get as much fun from your music as I have done with Hugo. 

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