Why would the digital optical output from my CD player be louder than that of my streamer?

I thought that a digital output audio signal didn't have volume info encoded in it; ie, that the bit depth tells you the dynamic range of recorded sound, from 0 to highest volume, but does not tell the downstream devices how loud the sound should be (ie, what you actually hear, in SPL).  In other words, the volume would be entirely determined by the preamp (after the DAC converts it from digital to analog), not by the digital output source.
But I'm finding that the digital (Toslink) output of my Cambridge CD player is noticeably louder than that of my Bluesound Node, after going thru the same DAC and preamp. Is my assumption of the digital signal having no volume info wrong?

@jond  - Do you mean the output voltage on the optical input on the DAC?  How would an optical signal pass voltage?

Can you connect the Bluesnode to your DAC via Toslink to compare? Maybe the Toslink inout on your DAC is louder than the USB. I am assuming that USB is how the Bluenode is connected.


Normally, I use the coax output (SPDIF) from the Bluenode to my DAC. Unfortunately, that’s not possible right now — the Coax output on my Bluenode crapped out this week. But you’ve given me an idea – I have a new DAC with a USB input, so I could use the USB output from the Bluenode to the DAC, and compare that with the optical output. I’ll let you know how it goes; thanks! 

I thought that a digital output audio signal didn’t have volume info encoded in it;

For normal stereo this is true, but HDCD and movie soundtrack break this somewhat. Generally not things you need to care about when playing CDs.

The amount of gain applied is entirely up to the device that creates the analog signal.

This also assumes neither player has a volume control. :)

My CD player is louder too. More voltage. Mystery solved.

Not so fast, @hilde45 -- The CD player is sending a digital signal to my DAC/Pre on Optical, and another digital signal to the same DAC/Pre on Coax; for both the volume is the same, but fairly loud.  Now I switch the cables to the Optical and Coax outputs on the Bluesound; again the sound levels are the same, but much less loud. How could higher voltage on the CD player account for that?

Are you streaming a local file that was ripped from the same CD?

I see a few possibilities.

1) The content from your steamer is a different mastering of the same album 

2) the streaming service is adjusting the digital levels as part of their delivery technology. 

3) The bluesound node incorporates a digital volume control and it's not actually bit perfect when the volume is at 100% or set to fixed. 


Interesting possibilities -- I especially liked #3, which made me think of a setting in the BluOS app that I hadn't played with before.  Under the app's Settings, if you go to the Audio tab they have a setting for Volume Limits (dB), that is set by default to a min of -80 and a max of -10.  I pushed it up the max limit to 0 dB, and voila, it's louder -- but now it's louder than the CD player! 

I have heard that Bluesound controls the volume by changing the number of bits per sample (if I'm wrong, hopefully someone on this forum will let me know), but I would expect that to affect the quality of the signal, not the volume.  Can someone set me straight?