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Objective measurements of DAC vs AMP volume control

Kumabear

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Hey does anyone have a link to a thread or reliable video that has objective data comparing the different out output qualities of an Amp when volume is controlled on the DAC vs when its controlled at the amp.

I tried searching the forum and found a few discussion threads but no real hard data.

I read that reducing volume on the digital side of the chain reduces bit depth which could have a detrimental effect on quality via a reduction of dynamic range headroom.

Does using a 32-bit DAC effectively solve this because you have the extra headroom there to allow for a reduction of bit depth without making an audible impact on quality?

I think it would be really interesting to see comparison data at different DAC bit depth's to show how it impacts amp output measurements on the analogue side of the chain, to see if there is a point where it doesn't really matter anymore.

Would also be interesting to see if different DAC chip's / DACs behave differently and are objectively better / worse.
 

RayDunzl

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My take:

On a 24 bit signal:

Traces represent the voltage output of some device - DAC or Amplifier, scale as needed.

First trace, no attenuation.

Second trace is the same as the first, but attenuated by 60dB, which is enough to take the sound from loud to all but inaudible in a reasonable listening level case.

Third trace - zoom in on the second trace to see what's still there. Note the linear voltage level is 1/1000th the original.

index.php


There's till about 14 bits of "depth" left, and you can barely hear anything because the volume is reduced that far.

This doesn't take noise into account, but the signal would appear to be only barely harmed if at all.

My conclusion:

Don't worry about it.
 
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Axel Endriss

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In difference to RayDunzl's finding in my case (Allo Piano 2.1 / Kali, Rasberry PI3 with Volumio V3.378) it's obvious without measurement that DAC volume control harms the sound quality if not set to 100%. Even though Volumio says that the "hardware control" does not affect the sound quality. Unfortunately, I believed that and it took me several years to figure it out. Possibly this can't be generalized, but in my setup it behave like this.
 
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Kumabear

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In difference to RayDunzl's finding in my case (Allo Piano 2.1 / Kali, Rasberry PI3 with Volumio V3.378) it's obvious without measurement that DAC volume control harms the sound quality if not set to 100%. Even though Volumio says that the "hardware control" does not affect the sound quality. Unfortunately, I believed that and it took me several years to figure it out. Possibly this can't be generalized, but in my setup it behave like this.
Keep in mind that in order to do a listening test for this you would need to be rapidly swapping between two complete identical setups and doing it blind to know for sure.

We will almost always perceive a louder volume to be higher quality.

To test this you would have to have two identical DAC and integrated Amps, have one setup to attenuate volume on the DAC side and one using the Amp volume control.

Set them both to the same measured volume then blindly swap between.

If you have not done this it's impossible to be sure, it's been proven time and again that our brains will trick us into hearing what we believe we will hear rather than what we are actually hearing.

If you are using a 24bit source file for example on a DAC set to 24 bit and then reduce volume to a normal listing level, you are probably still above 16bit CD quality even at the reduced volume. I'm Doubtful that especially at the lower volume the difference in fidelity will be audible.
 

Axel Endriss

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Keep in mind that in order to do a listening test for this you would need to be rapidly swapping between two complete identical setups and doing it blind to know for sure.

We will almost always perceive a louder volume to be higher quality.

To test this you would have to have two identical DAC and integrated Amps, have one setup to attenuate volume on the DAC side and one using the Amp volume control.

Set them both to the same measured volume then blindly swap between.

If you have not done this it's impossible to be sure, it's been proven time and again that our brains will trick us into hearing what we believe we will hear rather than what we are actually hearing.

If you are using a 24bit source file for example on a DAC set to 24 bit and then reduce volume to a normal listing level, you are probably still above 16bit CD quality even at the reduced volume. I'm Doubtful that especially at the lower volume the difference in fidelity will be audible.
I was suprised also because I haven’t expected this. However, I came to this when I connected a headphone amplifier. So far I had the headphone mostly connected to my laptop, so I expected a noticeable improvement. But what I realized first of all was that I could not achieve a proper volume. I mean I could make it loud enough for normal listening, but not really loud, which of course with a headphone amp should be no issue. Apart from this I noticed that the sound hasn’t improved compared to the laptop. Therefore I thought the amp is faulty and so I wrote an email to the manufaturer. Later on shortly before I switched it of and went to bed I realized that I had the volume in Volumio only at around 15%. After putting it to 100% I could blow my ears off
:slight_smile:
The further testing I have then saved for the next day. Before I continued I got the reply from the manufacturer which btw mentioned: “The best would be to have an item (DAC) without any volume knob on it and just let the amp do the thing. It is better like that since the DAC volume can greatly influence the quality of the sound that you want to hear.”. I tried this with the headphone amp and infact the sound improved dramatically. After a while of thinking about it I thought that this acutally needs to apply not only to the headphone amp but also to the normal amp. So I tried it and the differnce is so significant that one does not need to think at blind test.
What I’m not sure about and this might have an influence: I do have activated audio resampling in Volumio because for my DAC (Allo Piano 2.1 & Kali) this is requierd (because somehow the kernel doesn’t supports it, as far as i understood).
So far I usually set the volume level in Volumio at around 25% so that I had enough “space” for increasing it. So it applied to me often that I had this situation. Now with Volumio set to 100% it’s really close to black and white how much the difference is. Especially also if I listen at very low volumes.
All in all I have to say I’m extremely happy that I figured this out (by chance).
 
D

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DAC produces analog signals. If DAC volume is reduced, DAC just needs to produce weaker analog signals instead of reducing bit-depth by decreasing amplitude of digital bits.

That's my theory. But, DAC can still attenuate digital bits instead of producing weaker analog signals.
 

antcollinet

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DAC produces analog signals. If DAC volume is reduced, DAC just needs to produce weaker analog signals instead of reducing bit-depth by decreasing amplitude of digital bits.

That's my theory. But, DAC can still attenuate digital bits instead of producing weaker analog signals.
What would be the mechanism for a DAC to "produce weaker analog signals" in order to change volume? Are you talking about a buffered analogue potentiometer (In other words, and analog pre-amp) on the output of hte DAC?
 
D

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What would be the mechanism for a DAC to "produce weaker analog signals" in order to change volume? Are you talking about a buffered analogue potentiometer (In other words, and analog pre-amp) on the output of hte DAC?
If you set DAC volume to -16dB in operating system, the DAC could just produce weaker analog signals instead of massaging the bits.

Update: I guess a digitally controlled stepped attenuator in DAC. If that's too expensive, then you can just use 32bit floating point numbers or 64-bit floating point numbers or 32-bit integer in DAC.
 
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antcollinet

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If you set DAC volume to -16dB in operating system, the DAC could just produce weaker analog signals instead of massaging the bits.
How do you think it could do that, what circuit do you think would be used?

In any case, if you set volume down in OS, the OS simply changes the bits before sending to the DAC. Same effect as if the DAC does it.


EDIT - Let me help out here.

In order for a DAC to "produce a weaker analog signal" it needs an analog circuit after the DAC chip ouput. Most DACS don't have this - they simply ouput a fixed voltage for a fixed digital value. They do their volume contol (if they have it) in the digital domain.

Some (EG RME ADI2) has an analogue gain section in the analogue circuits. The RME solution gives it an ability to reduce the amount of digital change needed in 6dB steps (1 bit steps), so you don't need to lose more than 1 bit resolution as long as you only need around 30db reduction in volume.

There are also analogue volume contol ICs available (eg from Texas instruments) that provide the equivalent of a full digitally contolled analoge potentiometer. These are used by some AVRs or amplifiers for example, but I'm not aware of any DACs that use these.

However there is no way for the computer/OS to access these circuits - so they can only be used directly from the built in DAC volume control - if they are present at all.
 
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D

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How do you think it could do that, what circuit do you think would be used?

In any case, if you set volume down in OS, the OS simply changes the bits before sending to the DAC. Same effect as if the DAC does it.
DAC exposes its volume settings to operating system. Its setting persists across reboots. I verified that DAC retains its own volume setting and exposes it to operating system. If it retains its own internal volume setting, it can potentially operate a digitally controlled stepped attenuator at the output.

If a digital stepped attenuator is expensive, a DAC can resort to 32~64-bit floating point numbers or 32~64-bit integers for internal attenuation.
 
D

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2023-03-31 17:46:40.png

This is how Topping D10s exposes its own internal volume to my operating system.

This is hardware volume. Adding software volume to anything requires explicit configuration by me.
Hardware volume is used by default.

Software volume can be configured in applications or in your sound server software.
 
D

Deleted member 58865

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In any case, if you set volume down in OS, the OS simply changes the bits before sending to the DAC.
Every OS uses hardware volume by default. Adding software volume to your software mixer may require knowledge. Thus, you don't get software volume by default.
 

antcollinet

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View attachment 276168
This is how Topping D10s exposes its own internal volume to my operating system.

This is hardware volume. Adding software volume to anything requires explicit configuration by me.
Hardware volume is used by default.

Software volume can be configured in applications or in your sound server software.
Interseting - I wasn't aware of that mechnaism. However, that is still a digital volume control. The D10 does not have an analogue volume control circuit.

We seem to be discussing this in two different threads. Do you want to standardise?
 

charleski

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Interseting - I wasn't aware of that mechnaism. However, that is still a digital volume control
Yes, the picture kenji showed is simply the interface provided by alsamixer through the USB control descriptors. The actual volume control is happening in the ES9038Q2M DAC chip and is digital:
1680254626977.png
 
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