Help Understanding Roon DSP Volume vs. a DAC's Digital Velume

[Open Mind Audio]

Could someone who knows explain something that remains a bit of a mystery to me after reading many interesting threads here on DSP Volume, digital volume, attenuation and noise floors?

Does Roon's software-implemented DSP Volume function similarly to the digital volume in most modern, low-noise DACs? Or do these function totally differently?

I'm an avid listener and forum reader but not too swift with the electrical jargon, so the simpler the explanation the better (though feel free to go on longer than the standard John Yang epigram).

I'm asking mainly out of curiosity, after reading a lot on the subject, since some people seem to equate Roon's DSP Volume with "digital volume" control, at least in a general way.

I'm also curious because I use Roon's DSP Volume with my SMSL DO100 in a desktop setting and like the results. But Roon will not offer me the option of DSP Volume with my Oppo UDP 205, just "device volume."

Thanks.

PS - Roon still lets me set digital headroom on the output to the Oppo, and my understanding is that operates the same as their DSP Volume, so I get some DSP attenuation that way. I need the attenuation because the Oppo is connected directly to my Outlaw 2200 monoblocks driving Triton Ones (92 db senstivity). The result without attenuation is so loud that I would often be listening in the 20 range on the Oppo's device volume and can't get a quiet enough setting for conversation, even at volume of 1. That wasn't working for me. But the set up sounds better using Roon's digital headroom to knock back the output 12 db or more.

 

[Lambda]

Does Roon's software-implemented DSP Volume function similarly to the digital volume in most modern, low-noise DACs? Or do these function totally differently?

Its totally the same with most DACs.
Some DACs have internal 32bit processing and your DSP to DAC is "only" 24bit. so in there cases there might be a small benefit in lowering it on the DAC.

Also some DACs have Analog attenuators and don’t only aoftware volume control.

on the Oppo's device volume and can't get a quiet enough setting for conversation, even at volume of 1. That wasn't working for me. But the set up sounds better using Roon's digital headroom to knock back the output 12 db or more.

In this "extreme" cases you might better get a Analog XLR/RCA Attenuator.

If you uses 6-12dB of software volume controle you don't loses a lot but over 12dB is certainly not ideal.

 

[SKBubba]

It's my understanding that Roon converts everything to 64 bit float before applying any dsp, including volume. That's probably better than most dacs, plus it's using a much more powerful cpu.

 

[Open Mind Audio]

It's my understanding that Roon converts everything to 64 bit float before applying any dsp, including volume. That's probably better than most dacs, plus it's using a much more powerful cpu.

That's my understanding too, based on @DrCWO paper about The final truth about DSP Volume Control in Roon. Roon states that in the signal path info too.

 

[DVDdoug]

I your situation some analog attenuation is probably theoretically better...

When you lower the digital volume you aren't using all of the DAC's bits so you loose resolution, no matter how it's done. But with 16-bit data and a 24-bit DAC you can lower the 24-bit data going-into the DAC and still have the 16-bit resolution. I'd be surprised if there are any software volume controls working in 16-bits...

When you lower the analog level you also loose "usable resolution" because by reducing the signal you are lowering the signal-to-noise ratio.

It depends on where the noise is coming from... Usually the volume control is at the power amplifier input so any noise before that gets reduced along with the signal but any noise generated by the power amp remains. If you're not hearing any noise, the degraded signal-to-noise ratio isn't a problem!

When you are using a digital volume control as a "regular volume control" you don't normally hear any loss of resolution because the volume is lower and you can't hear the low-level "defects" in the lower resolution audio... If you are only using a couple of bits the volume is so low you can't hear ANYTHING anyway...

But where you get into trouble is when you re-amplify the signal (whether it was attenuated in digital analog). This is similar to what you are doing because you are using it as "permanent attenuator" as well as a volume control.


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If you want to do some listening experiments -

Open any good audio file in Audacity.
In Audacity set dither to "none". (Dither is added noise and it will foul-up the experiment.)
Export it as an 8-bit WAV file.
Run the Amplify effect at -48dB (actually attenuation).
Export this as a 16-bit file. (You are only using the "quietest" 8-bits.)

When you play the 8-bit file you'll hear the loss of resolution as quantization noise which is like a "fuzz" riding on top of the audio. It's similar to regular analog noise in-that it's most noticeable when the signal is quiet. But unlike regular noise it goes-away completely when there is digital silence.

When you play the very-quiet 16-bit file it's only got 8-bits of resolution but the quantization noise is down around -90dB like any 16-bit file and you won't hear it... No fair cranking-up the volume! Not yet...

If you do crank it up you probably don't have enough analog gain to hear it anyway. If you do hear noise when cranking-up the analog gain, remember that quantization noise goes-away with digital silence. If you've cranked it up and you are hearing noise, the quantization noise will go-away with silence so any remaining noise while paused is analog noise.

If you load the -48dB file back into Audacity and re-amplify it bu +48dB, it still has 8-bits of resolution and you'll hear the quantization noise just like the other 8-file.

Note that Audacity uses floating point internally so you don't loose resolution until you create a regular (integer) WAV file.

 

[Open Mind Audio]

I your situation some analog attenuation is probably theoretically better...

When you lower the digital volume you aren't using all of the DAC's bits so you loose resolution, no matter how it's done. But with 16-bit data and a 24-bit DAC you can lower the 24-bit data going-into the DAC and still have the 16-bit resolution. I'd be surprised if there are any software volume controls working in 16-bits...

When you lower the analog level you also loose "usable resolution" because by reducing the signal you are lowering the signal-to-noise ratio.

It depends on where the noise is coming from... Usually the volume control is at the power amplifier input so any noise before that gets reduced along with the signal but any noise generated by the power amp remains. If you're not hearing any noise, the degraded signal-to-noise ratio isn't a problem!

When you are using a digital volume control as a "regular volume control" you don't normally hear any loss of resolution because the volume is lower and you can't hear the low-level "defects" in the lower resolution audio... If you are only using a couple of bits the volume is so low you can't hear ANYTHING anyway...

But where you get into trouble is when you re-amplify the signal (whether it was attenuated in digital analog). This is similar to what you are doing because you are using it as "permanent attenuator" as well as a volume control.


-------------------------------------------------------------
If you want to do some listening experiments -

Open any good audio file in Audacity.
In Audacity set dither to "none". (Dither is added noise and it will foul-up the experiment.)
Export it as an 8-bit WAV file.
Run the Amplify effect at -48dB (actually attenuation).
Export this as a 16-bit file. (You are only using the "quietest" 8-bits.)

When you play the 8-bit file you'll hear the loss of resolution as quantization noise which is like a "fuzz" riding on top of the audio. It's similar to regular analog noise in-that it's most noticeable when the signal is quiet. But unlike regular noise it goes-away completely when there is digital silence.

When you play the very-quiet 16-bit file it's only got 8-bits of resolution but the quantization noise is down around -90dB like any 16-bit file and you won't hear it... No fair cranking-up the volume! Not yet...

If you do crank it up you probably don't have enough analog gain to hear it anyway. If you do hear noise when cranking-up the analog gain, remember that quantization noise goes-away with digital silence. If you've cranked it up and you are hearing noise, the quantization noise will go-away with silence so any remaining noise while paused is analog noise.

If you load the -48dB file back into Audacity and re-amplify it bu +48dB, it still has 8-bits of resolution and you'll hear the quantization noise just like the other 8-file.

Note that Audacity uses floating point internally so you don't loose resolution until you create a regular (integer) WAV file.

Thanks, that's helpful. I have some analog attenuation heading my way in the form of a Topping Pre90, arriving next week from Shenzen, so that's good to hear.

I'm still unclear on whether the Roon DSP Volume process (floating to 64 bits etc. before sending info to the DAC) is the same as the process that takes place when a good, low-noise DAC adjusts digital volume. But perhaps the explanation will be over my head anyway, so I should probably just focus on the music ....

 

[mdsimon2]

Thanks, that's helpful. I have some analog attenuation heading my way in the form of a Topping Pre90, arriving next week from Shenzen, so that's good to hear.

I'm still unclear on whether the Roon DSP Volume process (floating to 64 bits etc. before sending info to the DAC) is the same as the process that takes place when a good, low-noise DAC adjusts digital volume. But perhaps the explanation will be over my head anyway, so I should probably just focus on the music ....

Roon and DAC IC volume control are both digital and are essentially the same. Roon may be slightly better in terms of quantization noise but both will have quantization noise well below the analog noise floor of your DAC / amp.

Michael