A few nights ago a wrote a…let’s call it a ‘treatise’…comparing a little ChiFi tube buffer with the Darkvoice 336SE. In that post, I remarked that one of the oft-cited advantages of tubes is a spatial presentation (soundstaging & imaging) that makes tube amps/preamps often sound more “holographic” than their solid state counterparts. My own testing has confirmed such a phenomenon with relatively inexpensive gear. Don’t worry, I’ll do my best to keep this post shorter.
It’s uncontroversial to say that tubes distort the incoming electrical signal more than their solid state counterparts. Why then, if tubes mess with the signal so much more, are they able to create a better spatial presentation? I do NOT have a definitive answer to this question. Thus, this post is both throwing out some hypotheses and hoping to generate a discussion. I would really like to hear your ideas on this question. I came up with a hypothesis, tested it as best I could, and came up with an inconclusive result. I’ll share that here and hopefully you all will run with it.
Background:
First, to understand my forthcoming hypothesis, I need to define “distortion.” I’m going to take a fairly basic definition here. In the context of an electrical waveform it simply means to change the shape of that waveform. Electronic components can do this in a variety of ways, but that’s going to be the definition I run with here. Feel free to pick it apart - but please be clear why. Harmonic distortion (the HD in THD) is then changing the shape of the harmonic waves riding along with the fundamental oscillation.
Second, let’s talk about human hearing and how our auditory systems localize sounds. One of the primary ways (there are others) humans localize sound is through the changes in pitch and intensity and the time delay between our ears’ perceiving the sound. If a sound occurs to the left of our head, our left ear hears it first. Then, some small amount of time later, our right ear hears the same sound at a slightly lower pitch and intensity. The lower pitch is caused by the sound wave 1) diffracting around our head and 2) some of the energy from the compression wave passing through the matter of our heads producing a refracted waveform. Our brains take over and begin interpreting those pitch and intensity changes and time delays to give us an idea of where the sound is occuring (this is a type of pattern recognition, which I’ve also written some about here at HiFi Guides, sorry, I’m a hopeless academic). In this example, what our right ear hears is technically a distortion of what the left ear heard - the waveform has changed between left ear and right ear.
An Initial Hypothesis:
Since we can make the case that our localization ability relies on some degree of sound-wave distortion, maybe it’s reasonable to think that the pursuit of vanishing levels of distortion in our audio gear is having an adverse effect of the spatial presentations of gear. For example, our own @M0N was the first on this forum to point out that THX amps do not have the spatial presentation chops that the Rupert Neve RNHP has. Many of our fellow HiFiGuides (we need a denonym here) members have echoed his sentiments. According to Amir at Audio Science Review, the RNHP has much more distortion than the Drop 789 or the Monolith 887. The Darkvoice 336SE goes far higher yet. These distortion measurements and the nature of human-hearing-localization got me wondering if some amount of some type of distortion is helpful in creating sonic space. Is there a chance that some of the distortion that is introduced by tubes (or the type of distortion in the RNHP and other solid state devices that image well) mimics the distortion of the sound wave that happens because our heads are physically in the way of a sound wave? A working hypothesis was more or less yes, that.
There is a lot to unpack and measure here. I admit to limited knowledge on the ins and outs of total harmonic distortion and noise and SINAD, etc. I also don’t know enough to say what kind of distortion would mimic the diffraction caused by our heads being in the way of a wave. There are also lots of different kinds and sources of distortion that get collapsed into the singular THD and SINAD measurements. So again, I appeal to the community to fill in some of the inevitable holes in my knowledge and thinking. There is also a limited body of research that shows that tubes distort oh, so good, but that article does not mention the spatial presentation at all, and that’s what I’m interested in here.
The best test I can come up given the equipment I have access to is to use binaural recordings and compare their spatial presentations on tube and solid state gear. There are different methods of doing binaural recordings, but the one I’ll use is the type that uses a dummy head with microphones placed right at the openings of dummy ear canals (or in). When recording a live performance, this microphone setup will, to some degree, capture the subtle pitch and intensity changes that happen to the sound waves as they bend around the head. Traditional recording techniques either use 2 microphones spread several feet apart or use a mixing console to pan certain signals to one channel or the other. These traditional techniques capture or approximate 2 of the 3 ways our auditory systems process localization: time delay and intensity difference a the two microphone positions (in-room speakers would presumably do the third). Binaural recordings hard record the diffraction-caused pitch shifts. A super-clean, i.e. low-distortion, amplifier’s spatial presentation should equal or surpass a higher-distortion amplifer, like a tube amp, in spatial quality with binaural recordings. The low-distortion amp will more accurately reproduce those recorded distortions instead of introducing them on their own. A corollary, and in alignment with the theory that 0 distortion is the best, is that a high-distortion amplifier would NOT be able to produce as good as a spatial presentation as a low-distortion amplifier on a binaural recording - the ‘excess’ distortion would further damage the signal and possibly collapse the sonic image. Let’s test it…
Method:
Some time ago I downloaded a binaural music sampler from HD Tracks [Hey! It’s FREE right now!] and almost forgot about it until now. For one iteration of the test I split the SE output on my SMSL SU-8 DAC, sent one signal through my Douk Audio Dz tube buffer with GE JAN5654W tubes and then into a JDS Labs Atom amp, and the other signal went directly to the Atom. In the second round of the test I sent the SU-8’s balanced signal to the SMSL SP200 amp, and the unbalanced output through the tube buffer and into the RCA input of the SP200. I then played those binaural tracks and switched back and forth, paying particular attention to the soundstage and imaging. In the comparison post linked above, I discussed how the spatial presentation of the tube buffer bettered both of these pure solid state solutions. I used Beyerdynamic DT880-600 ohm headphones as they are reknowned for their spatial prowess at their price point.
Results:
Definitively, the imaging and soundstage from both the Atom and the SP200 equalled what the buffer did on these binaural recordings. The buffer still provided a warmer, more relaxed sound, but there was no longer any audible difference in the quality of imaging or soundstage. This result also means that the buffer’s spatial presentation, with its much higher distortion, was also not WORSE than that of the pure solid state presentations.
Discussion:
While the disappearance of the difference in spatial presentation between tube and solid state was definitive, the results here are not. This simple test does not show that it is the distortion a tube injects that mimics the real life, between ear distortion of real life soundwaves. This result does, however, provide some partial support to the hypothesis that the tube-caused distortion is helpful for spatial presentation. And really, that’s all I can conclude here.
I remind you all that due to my limited knowledge of the engineering side here, all of this might be flawed, and possibly flawed enough to be a pile of bovine feces. For example, a tube preamp/amp is going to distort the sound in both channels of a stereo setup in probably the same way and amount, whereas in real life, only one ear hears the distortion in sound. It’s possible this issue may be mitigated by the fact that stereo effects are created with time delays and differences in intensity, so the same amount of distortion in both channels creates a proportionally different impact in what each ear perceives, partially mimicikng the IRL pitch change. But, I can say with confidence that on my gear binaural recordings produced no difference in imaging or soundstage quality between tube and solid state.
So what do you all think? What’s going on here?
(was that shorter? 
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