FM3 S/PDiF routing / signal flow


I just received my FM3 and I am blown away by what it offers (even though I own the AXE-FX III).

At the moment, it is connected to a Lynx HiLo via S/PDiF, examining an issue with a pretty low input level led to the following findings:

• The FM3 S/PDiF output is dependent on the levels set on the OUTPUT LEVEL KNOBS 1&2.

• At full clockwise settings of the OUTPUT LEVEL KNOBS, setting OUTPUT 1 as S/PDiF OUT SOURCE is the only way to achieve the unity gain dBFS level that corresponds to the USB output. Switching the OUT 1 CONFIG output level between +4 dBU und -10 dBV does not affect this signal level.

• OUTPUT 2 as S/PDiF output source not only reacts to the OUTPUT LEVEL KNOB but also to the Boost/Pad settings in the OUT 2 CONFIG. Selecting 18 dB will result in the highest output level that can be achieved using OUTPUT 2 as an individual output, which nevertheless results in a 6 dB lower signal via S/PDiF than OUTPUT 1 in a similar configuration.

• As long as an Out2 block exists in the Scene/Preset, the OUTPUT 2 COPY setting in the OUT 2 CONFIG is not in effect.

• If no Out 2 block exists in the Scene/Preset, selecting OUTPUT 1 in the OUTPUT 2 COPY setting results in the same S/PDiF signal level as if OUTPUT 1 was selected as S/PDiF source. The master output level is still dependent on the OUTPUT LEVEL 2 KNOB (fully-clockwise for unity gain) and independent of the OUTPUT LEVEL 1 KNOB. No 6 dB drop in this case.

• The OUT 1 EQ and OUT 2 EQ settings in the Setup also apply to the signal transmitted via S/PDiF. These graphical EQ settings always apply to the respective outputs. This means that even if OUTPUT 1 is feeding OUTPUT 2 (OUTPUT 2 COPY setting), only the OUT 2 EQ settings would affect this signal.

Unfortunately, I couldn't find these details in the FM3 manual (maybe I overlooked them?), but the possibilities these smart signal flow options offer are absolutely amazing imho. For example, I can still have my headphones connected without blowing them up at full volume and still send a unattenuated S/PDiF signal via OUT2 and the copy option to my speakers (which are connected to the Lynx HiLo).

Now, it would be even more amazing if some Fractal Audio insider would shine a bit of light on the actual signal flow inside the unit. Are the OUTPUT LEVEL KNOBS 1&2 controlling a 32bit DAC or are these actual analog pots controlling an analog output that is sent through an additional AD conversion to feed the S/PDiF output?

Thanks a lot!
That's actually surprising. I haven't tried SPDIF on my FM3 yet, but on the AxeFX III SPIF out is unaffected by any of the output knobs (by default). I would've assumed the FM3 behaves the same way. Weird.
Indeed, it is pretty weird. And there's another little discovery:
The USB returns (1/2 + 3/4) are "hard-wired" to the respective outputs. So, when you're copying OUTPUT 1 to OUTPUT 2 neither USB 1/2 nor USB 3/4 are going out OUTPUT 2.
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