If USB sends a digital signal, why can you change the volume at the source?

[sygyzy]

I have a couple of small DAC's including a new Leckerton UHA-4. When I plug it into my computer via USB, I am able to make the music louder or softer by using the volume control in Spotify (or Windows). If it's just a signal, how is this possible? I thought a DAC just converts the digital signal to analog and spits it out, sort of line a line out for a DAP or the LOD for the iPod.

 

[mikeaj]

Change the volume settings, and the digital signal changes.  Specifically, the audio data is different.  At anything other than max volume, the volume is reduced by (pretty much) dividing each value by the same amount so they all become smaller by a certain factor.

 

[ProtegeManiac]

Quote:

If USB sends a digital signal, why can you change the volume at the source?

 
CDs are all digital but some CDs are louder than others. When you rip, you can set that up so you can have all your discs - particularly those from the "loudness wars" - at the same level that won't overdrive your components too easily. Digital has its own kind of gain control, except the db level is encoded instead of simply variable voltage or gain in the analog sense.

 

[sygyzy]

So are you guys saying that the "purest" signal you can get from a DAC is to set it at MAX volume through the source/OS/media player? And control the volume through the amp?

 

[ProtegeManiac]

Quote:

So are you guys saying that the "purest" signal you can get from a DAC is to set it at MAX volume through the source/OS/media player? And control the volume through the amp?

 
That's basically what everyone does and recommends. I'll leave the more technical details for someone else to explain as I already forgot. Now, for CDs that are recorded with too high gain, that's a different standard/method for why the signal strength is louder, and ideally it's better to just rip them then reduce the gain there.