Noisy optical input

[f1eng]

Thank you all for the input!

There was a previous thread where someone explained that 70 is the 0db level.

Ok, interesting... that might explain why I started hearing the noise around 80... I will give it a try again setting the volume to 70 and report back. However, if that's true, then what is happening when you pass the 0dB? I am assuming that 0dB is the full 24 bit resolution, so, how can you go above 24bit without any clipping? My original idea was that the digital volume control was simply controlling the voltage gain in the amplifier section, after the DAC, which always used the full 24bit resolution, but in another thread another user told me that's not what is happening, so, curious to know what is really happening...

I would expect your method of adjusting volume would be considerably inferior to using the volume control built into the ADH system which I believe to be a 32-bit system with dither, noise shaping and SAM compensation built in which will be working entirely wrongly (certainly in the bass) if you set the volume to 100 and then feed it a digital signal with most of the upper bits at zero to get the lower volume.
It sort of beats the object of buying a leading edge digital system in the first place. The RME is pretty antediluvian compared to Spark/ADH

I'm not that sure about that... If a software player uses dither and noise shaping also I don't see why the result would be that different, as long as I set up the volume in Spark to guarantee I have the full 24bit resolution (I see now I was wrong about this, I thought 100 would be the value to use and now I know it's 70). Since the DAC resolution is 24bits that will always be the limiting factor. If they were using a 32bit DAC then I guess the digital volume would be less critical at lower volumes... Furthermore, I don't get how the bass could be affected... If I got it right, SAM works at the frequency level, not volume, so, as long as the frequencies are not affected I don't see how the bass can be affected - unless they are applying DSP according to how the volume is set in Spark, and not by analyzing the income data level...

Regarding my RME card, I'm using it only to send the digital data to the Phantoms using its optical output for normal stereo, and has a hardware mixer for my movie watching, so I could mix the center and LFE channels on the Left and Right ones to feed my two Phantoms, so, I don't see how it could be limiting my sound quality (I have its volume always set to max).

Also, Have you compared playing in spark with the audio card?

I need to do it again more carefully, but from a quick comparison in the beginning I got the idea that the music volume was different when playing exactly the same files, which I found really strange... but like I said, I need to check it again more carefully before stating it, but if that's happening, then they might be doing something wrong when receiving the data from the digital input...

SAM does do level dependant DSP correction based on the power handling spec of the drivers. Setting a fixed 0dB level on the Devialet and adjusting the actual level elsewhere will defeat this capability (giving reduced bass since SAM will be protecting the drivers from a level much higher than the actual) and is almost certainly going to reduce potential sound quality anyway.