@052rc Thanks, but this does not appear to be what I experienced. I used SE connections from pre the Primaluna, and balanced to the Apollon. But both connections were the same type on each channel of the respective amps, and the gain switch was set identically for the two channels. Besides, the SE to balanced switch would result in a gain of 6dB. Here, the difference was 0.8dB, and was (unintentionally) introduced and later (intentionally) removed by software. It was this 0.8dB difference that shifted the image.
The physics and limits of relative loudness perception
I have recently been experimenting with the combination of tube pre / Class D power amplification; previously I was using all tubes. An interesting thing happened.
I switched from a Primaluna with EL34s to an Apollon Audio implementation of Purifi Eigentakt, to see what it would sound like. There was the immediate "this sounds kinda clinical" reaction, where the warmth of the power tubes was replaced by the more analytical sound of {solid state, Class D}. This was neither good nor bad itself, but a difference in presentation that took some time to adjust to. I also experimented with my HQPlayer settings (sent to a Pontus II OG), and arrived at a very pleasing tonality [comment: changing HQP filters and dither can alter the sound significantly, and was a lot simpler than auditioning 13 new DACs]. I found that, among other changes, the soundstage became more precise than with the Primaluna.
But... there was one very annoying thing: Singers who previously were front and center were now slightly off to the right. This was directionally consistent across multiple albums / singers / genres, although the exact degree of shift varied somewhat. I was racking my brain trying to figure out why. Turns out, when I was in my previous house, the system was set up in a non-rectangular room, and a previous set of adjustments using REW and HQP had resulted in the right speaker getting a gain boost of 0.8dB (just gain, no phase adjustment). It was on a different page of the HQP interface than the corrections for bass resonances, and I had missed it.
For a year in the new, rectangular, room, with the Primaluna, this did not appear to bother me. But it was glaringly obvious with the Apollon in the system. Once I found this vestigial setting and removed it, the singers swung back to dead center. Supposedly, our brains are not good at hearing under 1dB of sound difference, yet at 0.8dB this was very obvious. This leads to some questions, on which I hope those more knowledgable that I might help shed some light:
- Have there been any scientific studies done on how sensitive human hearing is to loudness in the determination of object placement in the soundstage? I.e., that you might not hear small relative volume differences, but these differences can be easily perceived via the imaging of the soundstage?
- Is it loudness, timing (i.e., phase), or a combination of the two that creates the sense of image?
- If so, is it a reasonable generalization that, at a similar price point / quality level, most (not all) solid state power amps will have better gain control or timing control vs. frequency than most (not all) tube power amps at that level? Or can different implementations of either topology have the better control of loudness/timing?
In any event, like several others in the forum, I am enjoying the combination of tube pre with Class D power. The HQP experiments with "warmth" have led me to order an LTA Aero, which is arriving in a few weeks. I think overall, the combo of new power amp / new DAC will be a nice improvement for my system. And it has been a great lesson in the importance of overall system synergy.
Any observations, references, or experiences would be much appreciated.
Showing 5 responses by sfgak
I found this interesting site: https://www.audiocheck.net/blindtests_level.php?lvl=0.5 I can, with 100% reliability, distinguish sound levels of +/-1.0dB. But only about 60% reliability for +/-0.5dB Clearly no "golden ears" here 😬 |
Thank you for the detailed response and the links to Erin’s videos. You provided me with a better vocabulary to describe what I experienced. Before I reframe that, the speakers are DALI Epicon 6, with a pair of asymmetrically placed Rythmik F12G subs. They have been carefully set up, including active crossover with the subs, and phase matching of the signals at the crossover points. All this can be viewed on my Virtual System page. The facts were:
Based on the new vocab you have given me, what I think was going on is:
I find the psychoacoustics interesting, in that the shift wasn’t really perceptible with the Primaluna, but was very apparent with the Apollon. I was pleased with the soundstage and imaging before, but even more pleased now. |
@mulveling Thanks for all your debugging tips -- lots of good info. Luckily in my case there was no underlying physical problem. It was just signal processing with the one channel’s 0.8dB gain. I found it very interesting that going to SS provided more precise image focus so that the problem was unmasked.
@larryi Yes, this is what I was really asking about in this post! Clearly, my setup context was way too detailed, but this is very surprising to me, too... I find it very interesting that volume deltas that we cannot hear on their own become easily discernible when hearing a "downstream consequence", for lack of a better term, like image shifts. I think it is the auditory analog of diffraction gratings. I can’t seem to find any research on the relative acuity for different kinds of sonic phenomena, like volume vs. image shifting. Anyone know of any? It makes me wonder if, for example, measures of image shift could be used to create some quantitative metrics that could describe what are currently qualitative descriptors like imaging and focus. Or perhaps to gauge whether the gain factors of initially-matched tubes are drifting apart over time. You might not notice based on other sonic qualities, but a periodic "image check" could help you make a determination.
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