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Digital volume control vs analog volume control

MrDamianOZ

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Hello,

I've been reading the forum for quite a while, but it's my first time posting, hoping to find a light in the dark about one subject that has been bugging me for a long time.

I've always been convinced and told by others, that digital volume control is a bad thing and that it decreases sound quality, because it alters the signal itself, rather than level of amplification.

And since I'm considering some updates to my stereo setup, I was trying to find a definitive answer to the question - do I need a preamp between a DAC and a power amp?
Most of the DACs I've been looking into have volume control integrated, but as far as I can tell, all of them do it digitally.
For now, I'm running Roon into Raspberry Pi 4 and then to Topping D30 (which I plan to upgrade at some point in the future) via USB, and from there to my old Denon PMA-100M (which definitely needs an upgrade, and will be the first thing in my setup to go).
When I decrease volume in the Roon app, I feel like the quality decreases slightly (the sound is less energetic), but I'm not sure if it's because of how Topping D30 reacts to lowering the volume in the app, or maybe it's just me making it up, by wanting to hear a difference to rationalize what I've been told my whole life.

So the question is - provided that I purchase a good DAC (let's say Gustard X16 or Topping D90, or something in this area of performance) and connect it via XLR to a power amp, will DAC's volume control be audibly harmful to sound quality and would it be beneficial to purchase a preamp (maybe Topping Pre90), or should I just not worry, and go straight from the DAC to the amp?

Thanks in advance for your help.
Best,
Damian
 
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Blumlein 88

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If your DAC does volume control in 32 bit float, 32 bit fixed or 64 bit, you really don't have to worry. Most good current DACs will be fine for you. Most volume control in playback software is fine.

I would not think the D30 vs Roon would sound any different at all.

There can be some edge cases where analog is going to work better for you or even part analog and part digital. However, like 99% of the time you can use a DAC with volume control and not have any issues. It is a non-problem.
 

PaulD

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There is an AWFUL lot of audiophile rubbish on the net about this, so please be careful

John Siau has the best and most complete explanation I have seen here:
https://benchmarkmedia.com/blogs/application_notes/13095789-volume-control-technologies

I would say that if your DAC and DSP is properly designed and dithered, it is better than a basic analogue part (ie a standard log pot). I certainly have not noticed any negative effects from a properly designed digital volume control, and I have no evidence that the Gustard is not properly designed. - oops, I see that B88 just beat me to it...
 
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MrDamianOZ

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Thank you for your replies.
Seems like I've been fed a lot of crap.

So technically, buying the Gustard X-16, or Topping D90, or something from SMSL in the same performance area should be a good point to start without having to worry? Great. I know what to do now, thanks :)
 
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Gregss

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Also, in at least one property the digital is likely to be better than most any analog pot used. Channel balance/tracking with volume changes.

Relay selected low tolerance resistors do do a good job at this if you must go analog.
 

lizhuoyin

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Thank you for your replies.
Seems like I've been fed a lot of crap.

So technically, buying the Gustard X-16, or Topping D90, or something from SMSL in the same performance area should be a good point to start without having to worry? Great. I know what to do now, thanks :)
My understanding is that each DAC has its best performance at 0dB with max. rms input. Using digital volume control in player software or DAC itself may be fine mathematically but the DAC performance will degrade during D to A if volume is too low. I am using digital volume control within 10dB to fine tune the volume and use a pair of u-pads (easy to get matched resistors) between DAC and my active speakers for desktop application. So far so good.
 
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Purité Audio

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Variable analogue output coupled to a properly dithered digital attenuator, just be aware when you attenuate digitally you turn down the signal not the noise whereas analogue attenuates both.
Keith
 
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MrDamianOZ

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On the other hand, digital attenuation usually reduces the (relative) distortion. If your goal is to maximise THD+N of the whole system, a combination of digital and analogue attenuation is likely to give the best result.

But that's the thing - I can't bear the thought of having two volume controls in my system. It just hits all the wrong spots in my brain. I'd like to have my audio setup as simple as possible - either DAC with volume control straight to power amp, or DAC without volume control (or one with software option to set volume to fixed, like some SMSLs do) to preamp to amp - and control the volume only in one place with one remote.

Which is why I'm wondering if the preamp is necessary in this scenario. But everywhere I turn, there are contradicting points of view. Even in the article sent by @PaulD, they say that
In most cases, a DSP-based volume control will limit the dynamic range of the playback system. This is because it doesn’t utilize the entire dynamic range of the D/A converter.
which doesn't sound that appealing.
 

mansr

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But that's the thing - I can't bear the thought of having two volume controls in my system. It just hits all the wrong spots in my brain.
If I were building a DAC and cared enough, I'd make a hybrid volume control that was transparent to the user. Obviously nobody wants two volume knobs.

But everywhere I turn, there are contradicting points of view. Even in the article sent by @PaulD, they say that
In most cases, a DSP-based volume control will limit the dynamic range of the playback system. This is because it doesn’t utilize the entire dynamic range of the D/A converter.
which doesn't sound that appealing.
That might matter if your amp and speakers are so sensitive that the intrinsic noise of the DAC is audible without attenuation. If not, as is usually the case, no overall dynamic range is lost.
 

the_hamster 2

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FWIW - no measurements, mind - I patched my Gustard A18 DAC directly to a legacy Carver amp, after setting Gustard vol. control at -30dB, then use the remote to fine-tune playback level when streaming (Hi-res)...repeated listening evaluation by interposing a Schiit SYS passive vol. controller between DAC and amp, setting DAC vol. @ 00dB, and streaming identical tracks at what I reckon was same vol. level...couldn’t tell any difference in SQ, but that’s me, YMMV.
 

jasonhanjk

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I'm actually quite curious.
What if I use:
a) 1k ohm pot and adjust to -20dB with a 2Vrms input VS
b) 1k ohm pot and adjust to 0dB with a 0.2Vrms input

Which one will have the better THD+N when both are 0.2V output?
Let me try a mock up circuit :D
 

PaulD

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Which is why I'm wondering if the preamp is necessary in this scenario. But everywhere I turn, there are contradicting points of view. Even in the article sent by @PaulD, they say that
>> In most cases, a DSP-based volume control will limit the dynamic range of the playback system. This is because it doesn’t utilize the entire dynamic range of the D/A converter. <<
which doesn't sound that appealing.

Just to add to what mansr accurately pointed out, not only is your system and room more limited in dynamic range than the DAC, but also the music does not use anywhere near the dynamic range of the DAC. So for all practical purposes, a properly dithered volume control is just fine. I can guarantee you that such digital gain adjustments were used throughout the recording and mixing process of your music with no ill effects.
 
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Blumlein 88

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Suppose your Dac had 120 db dynamic range which several of them do. If Max output results in 120 db spl, them you don't hear the noise floor of the dac. Then as you reduce volume digitally you technically have reduced dynamic range of the output but no noise or other artifact of this reduced resolution will be heard by you. Effectively the same as a perfect analog volume reduction.
 

jasonhanjk

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Below is a picture of a voltage divider mimicking a 1k ohm potentiometer.
It uses 5% part carbon resistor.
The measurement system input impedance is 100k ohm.

First, I measure the DAC Amp output at 0.992Vrms.
Result A is 0.00060% THD+N

Then I measure point B; 0.194Vrms.
Result B is 0.0070% THD+N

Lastly measure point C with reducing output of DAC Amp to match amplitude of 0.194V.
Result C is 0.0018% THD+N

From this simple experiment, using digital gain is better by 11.8dB THD+N over the 1k ohm pot.


Since I don't own any HP amp with pot control, that's the best I can do.
I'll let someone who have a commercial unit to verify my finding.;)

1k pot effect on THD+N.png
 

bennetng

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RayDunzl

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My experience with Digital Volume Control:

By the time I turn the volume down far enough where I might audibly notice a problem the volume is so low I can't hear anything being played anyway.
 
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lizhuoyin

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Below is a picture of a voltage divider mimicking a 1k ohm potentiometer.
It uses 5% part carbon resistor.
The measurement system input impedance is 100k ohm.

First, I measure the DAC Amp output at 0.992Vrms.
Result A is 0.00060% THD+N

Then I measure point B; 0.194Vrms.
Result B is 0.0070% THD+N

Lastly measure point C with reducing output of DAC Amp to match amplitude of 0.194V.
Result C is 0.0018% THD+N

From this simple experiment, using digital gain is better by 11.8dB THD+N over the 1k ohm pot.


Since I don't own any HP amp with pot control, that's the best I can do.
I'll let someone who have a commercial unit to verify my finding.;)

View attachment 114094
Nice test. I am wondering if increasing R2 to 5k ohms or using balanced U pad will improve the THD+N or not.
 
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restorer-john

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Obviously nobody wants two volume knobs.

Some of us want more than just two.

My power amplifiers pretty much all have input attenuators, the preamplifiers have adjustable gain and the sources also can be fixed or variable. Some of my preamps have twin gain and master controls (Kenwood L-07c).

If you want the best volume range and lowest noise all around, multiple stages, optimised for gain/noise are needed. There is no one size fits all, particularly with sources of all different levels.
 

mansr

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Some of us want more than just two.

My power amplifiers pretty much all have input attenuators, the preamplifiers have adjustable gain and the sources also can be fixed or variable. Some of my preamps have twin gain and master controls (Kenwood L-07c).

If you want the best volume range and lowest noise all around, multiple stages, optimised for gain/noise are needed. There is no one size fits all, particularly with sources of all different levels.
Wouldn't you prefer a single knob that magically adjusted all the different stages optimally for the desired level?
 
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