Fixed vs Variable output

[LegionOfHell]

Standalone DACs with no volume knobs usually have a fixed output when you set their volumes to max in Windows. Which is usually around 2Vrms ? For example, To use Atom DAC+ and SMSL SU-1 DACs you have to set their volumes to max in Windows and then they both output around ~2Vrms ?

(By DAC/AMPs I mean combo units like: (Topping DX5 , Creative G6/X7 , FX-Audio DAC-X6 MKII)

With Some DAC/AMPs, The volume knob affects the RCA-outs and with some, it doesn’t. some even have a switch to change between fixed and variable output.
Is my understanding correct ? please confirm.

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I have some questions:

Why do some DAC/AMPs have variable output through their RCA-outs that is controlled by the volume knob ? When using them as DACs only, why don’t they just output a fixed signal (~ 2Vrms) like a standalone DAC ? Does turning the volume all the way to zero makes the DAC/AMP to output a fixed signal ?

Doesn’t the signal get degraded when the output is variable ?

When used as DACs only(USB-Optical to RCA-outs), Do the following units output a fixed or variable signal:?

Creative X7
Creative G6
FX-Audio DAC-X6 MKII
Zorloo ZuperDAC

 

[staticV3]

Which is usually around 2Vrms ?

For RCA DACs, yes.

For example, To use Atom DAC+ and SMSL SU-1 DACs you have to set their volumes to max in Windows and then they both output around ~2Vrms ?

Usually, yes.
The exception is if your DAC does not support UAC2 Hardware volume control and you're using the ASIO or Wasapi Exclusive API to play.
In that case, the DAC will output the full 2Vrms with Windows volume set to anything from 1 to 100, and it'll be muted with Volume 0.

With Some DAC/AMPs, The volume knob affects the RCA-outs and with some, it doesn’t. some even have a switch to change between fixed and variable output.
Is my understanding correct ? please confirm.

Correct.

Why do some DAC/AMPs have variable output through their RCA-outs that is controlled by the volume knob ? When using them as DACs only, why don’t they just output a fixed signal (~ 2Vrms) like a standalone DAC ?

Because they attenuate the signal in the digital domain, before the DAC. The analog, attenuated signal is then sent to both the Line out and the built-in Amp, or to just one of them using relays.

Does turning the volume all the way to zero makes the DAC/AMP to output a fixed signal ?

Turning either the Windows volume or the DAC+Amp's volume to zero will usually mute the device.

Doesn’t the signal get degraded when the output is variable ?

Not in any way that can affect your listening experience, since modern DACs have so little noise that the bottleneck is generally elsewhere.

 

[LegionOfHell]

Because they attenuate the signal in the digital domain, before the DAC. The analog, attenuated signal is then sent to both the Line out and the built-in Amp, or to just one of them using relays.

Such DAC/AMPs have "infinite" volume knobs, Like Creative G6/X7 ?

How about FX-Audio DAC-X6 MKII ? Does it attenuate the signal in the digital domain ? (it seems like it also has an infinite volume knob?)

When the signal is attenuated in the digital domain , we say the unit has digital volume control , right ?

 

[staticV3]

Such DAC/AMPs have "infinite" volume knobs, Like Creative G6/X7 ?

Correct. They usually use rotary encoders instead of potentiometers.

When the signal is attenuated in the digital domain , we say the unit has digital volume control , right ?

Yup!

 

[DVDdoug]

There's sort-of a difference between "permanent attenuation" and everyday "volume control".

If you have 16-bit audio and you reduce the volume by 48dB (that's a LOT) you are down to 8-bits. With everyday volume control, or with a fade-out or quiet passage in the program, that's OK and you can't hear the loss of resolution. By the time it fades to below where you can hear it you can't hear anything, much less judge the sound quality.

But if you are down to 8-bits and you re-amplify to full-normal volume, you'll hear quantization noise.

If there is always attenuation and you are never using the full bit-depth it's more of a concern, but a moderate amount of attenuation is usually fine and it often comes-down to convenience.

If you start-out with 24-bits and reduce the volume by 48dB, you've still got 16-bits ("CD quality").

Something similar happens with an analog control... You're lowering the signal while any noise from the following amplifier/circuitry remains and the signal-to-noise ratio is lowered. If you attenuate line-level to microphone level and then re-amplify through a microphone preamp, you'll probably notice the loss of quality.

 

[earlevel]

If you have 16-bit audio and you reduce the volume by 48dB (that's a LOT) you are down to 8-bits. With everyday volume control, or with a fade-out or quiet passage in the program, that's OK and you can't hear the loss of resolution. By the time it fades to below where you can hear it you can't hear anything, much less judge the sound quality.

First, I agree with your post overall, just expanding this one part...

Accept for special cases, we're dealing with 24-bit DACs these days. And assuming the digital control is not flawed (low precision multiplies, for instance), reducing volume by 48 dB (~8 bits, which is what you're going for here), you are not "down to 8-bits." You still have 16 bits, because the lower 8 were unused. (I assume you're talking about digital volume control, since you referred to it by number of bits, and not a reference to the analog noise floor.)

Of course, at full volume (maybe a little bit over more peoples' comfort zone), you can hear all of those 16 bits without the digital volume reduction, and at -48 dB half the "bits" are indeed likely lower than you can hear, and I think that was your point. Though all 16 bits are still there.

But I agree with your advice, it doesn't really matter whether you use digital or analog volume control. Though you probably don't want to juggle both. There is some minor gain-staging for digital control, but it's just setting the analog to as loud as you normally care to listen—not lower for the obvious reason, and not higher because you might just be raising your noise floor needlessly.

Some people are unduly paranoid about digital volume control in modern DACs. I love having that Topping DX7 Pro knob in front of me to twist up of down (computer USB -> DAC -> powered monitors with max volume knob on backs), or use the remote, without an unnecessary analog preamp between.

 

[LegionOfHell]

Because they attenuate the signal in the digital domain, before the DAC. The analog, attenuated signal is then sent to both the Line out and the built-in Amp, or to just one of them using relays.

When using the DAC/AMP combo as a DAC only(USB-in / RCA-outs), Should the volume be set to max in windows ? if set to max, Will it output a standard ~2Vrms through RCA-outs just like the Atom DAC+(we have to set the volume to max for Atom DAC+ too) ? if so, it behaves like a fixed output and there won't be any signal degradation ?

What if the unit is being used through optical-in and not connected to a PC, Can/should the volume be set to max this way ?

With units that have digital volume control, the line-in doesn't go straight to the headphone amp section, it goes through ADC, DAC and then the headphone amp section. This is because of the digital volume control, right ?

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Some DAC/AMPs bypass the amp section when you max the volume in windows(Zorloo ZuperDAC) ... is this because there is only one analog out for both headphone out and line out ?

 

[AnalogSteph]

Why do some DAC/AMPs have variable output through their RCA-outs that is controlled by the volume knob ? When using them as DACs only, why don’t they just output a fixed signal (~ 2Vrms) like a standalone DAC ?

Because that would mean they'd need separate converters for both outputs, which is a matter of $$$ if nothing else.

With units that have digital volume control, the line-in doesn't go straight to the headphone amp section, it goes through ADC, DAC and then the headphone amp section. This is because of the digital volume control, right ?

You'll generally find either a digital volume control or an analog line-in, not both at the same time. If would be feasible, of course, that's what every DSP speaker does.

BTW, you may have noticed that decent DACs these days are kind of giving a lot of dedicated preamps a run for their money in real life. They'll undercut what used to be considered a good residual noise level and don't have any issues with output noise depending on where the volume pot is set either. With the now-standard 32-bit processing, digital attenuation is better than an analog pot could ever hope to be. Even at 24 bits and with the lowest-noise music material around, you'll probably have 40+ dB of leeway before losing any resolution at all, meaning that your greatest concern is going to be the analog noise floor.

 

[dualazmak]

I assume that OP's point and concern would be more or less related to "Where to control master volume during our usual audio listening sessions?", is it right?