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Foobar2000 + RME ADI-2 DAC gain staging help needed!

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I'm thinking of buying the RME ADI-2 DAC.

Currently I'm using (and will be using) Foobar2000 as the source and use ReplayGain with a -6 dB setting on the RG preamp (the negative value required for several of my classical albums). From the DAC, I'm outputting to a Yamaha A-S1000 integrated amp via its CD in.

The questions:
1) Is the outcome identical, if I set the negative -6 dB gain on the ADI-2 DAC instead and leave Foobar2000's RG amp at +0 dB? I'm guessing it must be because it's "just" digital attenuation.
2) ....which leads me to the gain-staging question: if I set the gain from 0 dB to -6 dB in the ADI-2 DAC, can I likewise up the Reference Level from +7 dBu to +13 dBu? I've tried using online calculators but I'm still not sure if -6 dB with +13 dBu is the same output voltage as 0 dB with +7 dBu. The (potentially?) higher Reference Level is the reason I'm thinking it would be better to leave Foobar2000 at 0 db and attenuate on the RME instead.

EDIT: Umm, I think maybe it should be +1 dBu and NOT +13 dBu, because the volume is lowered and needs boosting??
 

AnalogSteph

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Even at +7 dBu, ADI-2 DAC output noise is -122 dB(A) down, i.e. -117 dBV(A) (vs. -120 dBV(A) at -1 dBu). At the same time, A-S1000 input noise comes in at -98 dB(A) down from 150 mV, that's ca. -114.5 dBV(A). Using +7 rather than +1 dBu is going to cost you at most a whopping 0.8 dB more noise... and I have a feeling you're generally going to set the volume on the amp such that either would be disappearing below the amp's residual noise floor of 73 µV(A), which it would for an amplifier gain of around +30 dB, or approx. 15 dB below maximum volume. (And that's assuming amplifier output noise floor hasn't increased over minimum volume by this point, which it well might have. Now whether you care would be a matter of speaker sensitivity.) At this gain, even +1 dBu out would drive the amplifier to maximum power. I would choose +7 dBu at correspondingly reduced amplifier volume.

The RME really has more than ample dynamic range for use as a simple line-level DAC - it is, after all, well capable of driving a power amp on its own. You can easily leave yourself some headroom without issues. If push comes to shove, there still is the Auto Ref Level feature which will pick a ref level based on volume setting.

RG pre-gain has one key advantage: It lives in the world of floating point audio samples that have no practical upper bound on amplitude, however these are generally converted to integer samples in the audio stack at the latest, where the usual 0 dBFS limitations apply. Therefore, RG +6 dB and DAC -6 dB is not generally equivalent to RG -6 dB and DAC +6 dB. This is exactly why RG can be set to "prevent clipping", which uses stored peak amplitude to reduce gain on tracks / albums that would otherwise go beyond fullscale. The practical implication is that high dynamic range material will be playing correspondingly quieter. This may be a worthwhile compromise if you only have very few critical recordings affected by this.

If you're a fan of Mahler symphonies, for example, you may want to set RG pre-gain as low as -5.3 dB in order to cover all edge-cases without having to compromise on playback volume uniformity (the biggest offender in my collection being No. 10 / Berlin Philharmic / Sir Simon Rattle / 2000). There is little doubt in my mind that you could afford this given your equipment, but of course you may not even have any recordings this demanding to begin with. If in doubt go through your collection and identify all albums with both substantial positive RG album gain and peak amplitudes near 1.00; the required minimum pre-gain value = 20log(album peak) - (album gain).

It be noted that having some extra headroom may still be warranted e.g. when using the RME's parametric EQ.
 
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Thanks for the detailed answer, AnalogSteph!

I've cross-checked max true peaks (using both Foobar and Reaper) and RG album gains of my whole collection and manually adjusted a good bunch of the album RG values so that not one album peaks over +5.8 dB (I only use album RG mode). This was just an arbitrary limit that felt sensible to me. Some stuff is supposed to sound quiet - yet a few albums by Arvo Pärt and Morton Feldman had RG values way past +20! What a hiss-fest, lol... I deliberately don't use the prevent clipping feature (I don't trust it?), I like to set the RG preamp to a fixed -6 dB instead.

This being the case, isn't -6 dB on Foobar's RG preamp resulting in exactly the same output volume as a fixed -6 dB volume on the ADI-2 DAC? Further still, utilizing the RME's headroom for overs, I could even set the volume on the ADI-2 DAC to -4 dB and Ref Level up to +13 dBu. The output volts from the RCA outs would still be below the 2.8 volts input limit on my Yamaha. And enough headroom for those ~+6 dB momentary peaks.

I most likely would be using EQ only for my AKG k701 phones. I do have an Arendal S 1961 active sub with its own EQ that I feed from the Yamaha amp's pre outs. (Pretty easy to integrate with the ATC SCM11's, even with the mains running full as they're sealed and a bit bass shy.)

For what it's worth, the volume pot on my Yamaha A-S1000 is only at about 11 o'clock. No hiss or hum.
 
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