For complicated reasons I'll describe below, I decided to turn the gain up on all 3 Emotiva Stealth DC-1 DAC's I use in the living room system by 4dB. The current levels are
Tweeters: +10dB
Subwoofers: -11dB
Panels: +2.5dB
It's actually become extremely convenient that these DAC's have 0.5dB resolution gain switching that goes way down and up to +12dB. Functionally it's like getting a preamp with your DAC. Though purists might rather have their own high end preamp, the gain here is provided by an impeccable LM4562 with a 2005 generation digital level control (that was when they got about as good as an LM4562). If I ever switched to another DAC w/o gain, it might be difficult. But now thanks to fixed digital rate of 48kHz from the miniDSP (and 96kHz for the tweeters) I can simply time align the DAC's (and the speakers) for these fixed rates and it's done. (Previously, where the rates could vary from 44.1kHz to 96kHz...causing different delays in different DACs, it was impossible.) So, I can fairly easily use different DACs on each way of the system...but few have the nice digital level controls of the Emotiva and with 12dB extra gain.
The actual tweeter (crossing in at 20kHz) levels are so low that boosting the gain there is never going to cause the DAC to overload...or the following amplifier. The SVS subs are just very sensitive and I have their local level controls turned down also. The DAC feeding the Hafler 9300 driving the panels had one time been at -6dB so I could set the higher gain Aragon to 0dB. The Aragon is currently offline because the DAC feeding it now needs repair. Just before this latest adjustment shown above, the DAC feeding the Hafler had been turned to -1.5dB.
Well I decided to do this after seeing that even turned all the way up, to no digital attenuation on my Tact, I was getting peak levels at -87dB C weighted. That's not very loud. But you'd think at "0dB" it would be.
But when I was setting up the miniDSP for the midrange, I detected clipping problems if I set it's input gain control above -4dB (so ultimately I chose -6dB to be on the safe side of no digital clipping). This is because the miniDSP use a 48kHz ASRC input for the digital input. Such asynchronous sampling can be pushed into clipping by "inter sample overs" because there can be (and are, on many pop recordings) peaks up to 6dB (theoretical maximum) higher than the nominal level. This is another reason why units with SPDIF or AES digital input and digital output should use SYNCHRONOUS not ASYNCHRONOUS transmission. Asynchronous should only be used, if at all, in a terminal DAC unit which does not output digital. But totally unwarranted fear of JITTER has led to the near abandonment of synchronous digital receivers, despite the fact that the better ones did a nearly impeccable job with typical low jitter levels and considerably beyond.
The 1999 Tact RCS 2.0 did in fact have synchronous digital in and out, at rates from 44.1kHz to 96kHz. My living room system uses this as source pre-selector (to the input of the home-controlled switch, which switches between FM and everything else, and from there on to a splitter to the 3 miniDSP's) and level controller. I don't find the DSP in the Tact system meets my needs, with a trifle re-programming it could. The Tact preserves the input rate--and timing--from input to output. There might be some smoothing in the timing, I'm not sure of the details actually. But if I were to build something, I'd have it like this. I'm unsure if the synchronous receivers are made anymore. Or updated to 192kHz, which I don't consider of much importance. Actually my miniDSP's are limited to either 48kHz or 96kHz anyway. So it would be useless to lust over a front end controller ("digital preamp") with more than 96kHz anyway. And as I've many times stated, I think all that's needed is 96kHz, everything above that is a WOMBAT (Waste of Money, Brains, and Time). Peter Aczel and the near entirety of "Objective" audiophiles would say 44.1kHz is enough and that nobody has "proven" otherwise in reproduced blind testing. But I'm allowing margin over 44.1, for various reasons, though I recognize that 44.1kHz sampling can be damned good (and likewise 16 bits) and the vast majority of what I listen to is just that, and I'm still often (and pretty much always nowadays) wowed and so on.
So, the unfortunate loss of 6dB gain in my digital processing means I have to make up the gain somewhere. If I were to increase the output of the Tact, I'd get actual digital clipping (not just intersample overs) at the miniDSP inputs. So the only thing to do is to raise the output "after" the digital conversion. Which I can conveniently do with my Emotiva Stealth DC-1's because in fact the level control can be increased to +12dB.
But what happens with a digital signal at 0dB with the Emotiva at +12dB. Distortion rises from 0.0005% to 0.02% which doesn't matter audibly. That's because the output circuitry of the Emotiva can actually drive 25.65dBu (14.85V RMS) ! (Well, that's into balanced...) The output with the control at 0dB is 14dB, or 3.88v RMS, into 4 ohms, which is a bit low for some high end power amps, but you can crank it up.
I got that information from this Pro review. Pro's are interested in these sorts of things, which often don't get tested by audiophile reviewers. (John Atkinson always tests maximum output level, but it seems Amir did not, he simply tested with the level control at 0dB which is not the maximum.)
In unbalanced I likely have half the output, or about 7.92V, which is still almost 11.95dB higher than the standard output of 2V with the level at 0dB. So I can crank the level up to at least 11.5dB without concern basically (at least as far as the DAC is concerned), even if perchance there were a maximum digital level signal. (Perhaps to allow for inter-sample overs in the DAC itself...it might not be a bad idea to keep the level below +6dB for ultimate fidelity.) In my case, where the signal itself is deliberately -6 dB, I'm good with the 11.5dB level even before intersample overs become an issue.
The amplifier has "headroom" (above it's 1.1V rated input for full output) and besides such signals are way below the average level, due to both the mandatory -6dB processing reduction, and the crossover itself. If the amplifier is working too hard, I will hear it, just like someone with an all analog setup. What I strongly want to avoid is "invisible" digital clipping from ASRC for example.
Basically the signal is never going to go to the peak level (for one thing it can only go to -6dB on average) and the panels only get frequencies above 120 Hz, which also reduces the level. If there ever is a transient peak (which is all it could be above the -6dB level because of my miniDSP attenuation) it won't stress the analog at all.
Well now that I've checked the Emotiva capabilities, I'm thinking of cranking up the DAC's another 2dB.
