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Digitally reducing volume when connecting DSP directly to power amplifier

Rubberducky

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My current setup takes all its different inputs into a MiniDSP 2x4HD which acts as my DAC, and the output is connected directly into the power amplifier (main in) of my NAD C352 (80W per channel).

Volume is controlled on the DSP. Currently, to get output volume at 0dB on the DSP that's not too loud, I apply -10dB gain to the output channel of the DSP.

My first question is: I've read different things about digital gain reduction. Is it the case that this will not be a problem on modern devices?

I'm thinking of upgrading the amplifier to a bigger one since I assume my speakers could use a bit more power for the peaks (~120W per channel or more).
However, does this mean that if I again bypass the preamplifier and connect the DSP into a beefier power amplifier that I will have to reduce the gain digitally even more? Would this make sense to do?

Thanks up front for your insights.
 

abdo123

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the 2*4 HD outputs 2 Vrms at full output, you need to check what is the input sensitivity of your new amplifier (how much voltage input is required to drive it to full power). If it's below 2 Vrms then yes the master volume need to go down a bit. for every 6 dBFS reduction you take away half the voltage output.
 

MaxRockbin

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I use the DDRC-24 version of the same 2x4HD MiniDSP, using it as my DAC just as you describe. My MiniDSP volume is typically at around -14 to -22db with my pre-amp/amp (Pioneer SC-91 AVR) pretty much cranked - to what it reports as "0db" level. I think that gives the broadest dynamic range. It sounds good to me, but I've done no testing and I'm no expert.

BTW, if you are still using the remote that came with the MiniDSP for volume, it's worth investing $13 or so in a cheapo generic universal remote. My dog ate my MiniDSP remote and I'm glad she did. The volume control seems to work faster so it doesn't take so long to make significant volume changes. You also can program whatever buttons you want (depending on remote) to toggle sources etc. One thing I don't think is in the manual: You want to set the universal remote to send "SONY" signals. Whatever is the first listed Sony code in the remote manual is probably fine.
This is the one I bought, but I don't think it matters much:
GE universal remote Amazon link no affiliate
 

DVDdoug

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IMO it's "risky" to rely on digital volume control unless you're listening to low-power computer speakers or something where you're not going to hurt anything or annoy yourself and everybody in the house...

NAD C352 (80W per channel).

...since I assume my speakers could use a bit more power for the peaks (~120W per channel or more).
My handy-dandy spreadsheet says 120W would only be +1.76dB.

It's easy to remember that +3dB is twice the power*, +6dB is a factor of 4, and 10dB is a factor of 10.

I really wish more amplifiers had a peak power meter, or that you could buy an affordable peak power meter. Someday I may build one for myself.**

However, does this mean that if I again bypass the preamplifier and connect the DSP into a beefier power amplifier that I will have to reduce the gain digitally even more? Would this make sense to do?
Not necessarily. A higher power amplifier doesn't necessarily have more gain. If a manufacturer makes a series of similar amplifiers with different power ratings they often all have the same gain.



* There is a different formula for digital levels or signal voltage. +6dB is twice the digital level or voltage. ...If you double the voltage to a speaker (+6dB) the current also doubles so that's 4 times the power.

** I've made a giant LED VU meter effect, but it works at line-level and since it's just for show it's intentionally uncalibrated and it automatically adjusts itself for lots of "meter action" no matter how loud I'm listening.
 
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Rubberducky

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Not necessarily. A higher power amplifier doesn't necessarily have more gain. If a manufacturer makes a series of similar amplifiers with different power ratings they often all have the same gain.

Does this mean that the input sensitivity needs to be different then? The higher powered amp will then need to be able to hand higher power inputs into the power amplifier?
 

abdo123

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Does this mean that the input sensitivity needs to be different then? The higher powered amp will then need to be able to hand higher power inputs into the power amplifier?

not necessarily, it could be different and it could be the same.

It all depends on the engineer.
 
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Rubberducky

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not necessarily, it could be different and it could be the same.

It all depends on the engineer.

But for a given power amplifier sensitivity, doesn't increasing the power automatically increase the gain? And if two power amps have the same gain, doesn't the higher powered one need to have a higher input sensitivity? Or am I missing something?
 

abdo123

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But for a given power amplifier sensitivity, doesn't increasing the power automatically increase the gain? And if two power amps have the same gain, doesn't the higher powered one need to have a higher input sensitivity? Or am I missing something?

I copied this formula from the Hypex documents to help you better understand the relationship between rated power, gain and input sensitivity.

1625081143900.png
 

abdo123

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IMO it's "risky" to rely on digital volume control unless you're listening to low-power computer speakers or something where you're not going to hurt anything or annoy yourself and everybody in the house...

I have loudness normalization enabled where ever I can and I haven't run into any accidents yet.

Honestly I find it difficult that anyone has a pleasent continious listening experience without loudness normalization in 2021.
 

Plcamp

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But for a given power amplifier sensitivity, doesn't increasing the power automatically increase the gain? And if two power amps have the same gain, doesn't the higher powered one need to have a higher input sensitivity? Or am I missing something?

I would expect two power amps with same gain to output same power level at a given input voltage, and therefore the higher powered amp would require more preamp voltage to achieve max output. You would have higher headroom for the driver powered by the bigger amp, but given the lower power amp needs to be limited so 0db does not clip it, the smaller amp would determine the dsp gain adjustment to fully drive it at 0 dB?
 

Kal Rubinson

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Honestly I find it difficult that anyone has a pleasent continious listening experience without loudness normalization in 2021.
Depends on what you listen to and how you listen.
 
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Rubberducky

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Okay, the amplifier calculations are clear to me, thanks all!

Any other input on the digital volume attenuation? The speakers both get always -10dB + the actual master volume, which is typically between -20dB and -10dB. So I'm attenuating by 20dB to 30dB in general. Would this for some reason be worse for the sound than having a preamplifier doing analog attenuation when not using a DSP?
 

mdsimon2

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Okay, the amplifier calculations are clear to me, thanks all!

Any other input on the digital volume attenuation? The speakers both get always -10dB + the actual master volume, which is typically between -20dB and -10dB. So I'm attenuating by 20dB to 30dB in general. Would this for some reason be worse for the sound than having a preamplifier doing analog attenuation when not using a DSP?

Are you implementing any boosts in your DSP? Or is the 10 dB cut just to limit max volume level?

To me the test is do you hear any noise when nothing is playing? If you cannot determine if the device is on or off from your listening position digital volume control will do no harm because the noise floor is already below your hearing threshold. That being said the cheaper miniDSP devices do not have exceptional analog performance and you can run in to noise issues with higher sensitivity speakers and higher gain amplifiers. This forum talks a lot about SINAD but to me noise is much more important than distortion. It is pretty easy to pick out a high noise component but it is not so easy to pick out a higher distortion component (look at recent SMLS M500 THD issues as an example!). Now, whether that noise actually deteriorates your listening experience is another question but low noise equipment certainly helps ease the audiophilia nervosa.

If you can hear noise and you do not use maximum volume on your digital volume control you can certainly install some cheap line level attenuators to help maintain your SNR.

Michael
 
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Rubberducky

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Are you implementing any boosts in your DSP? Or is the 10 dB cut just to limit max volume level?

To me the test is do you hear any noise when nothing is playing? If you cannot determine if the device is on or off from your listening position digital volume control will do no harm because the noise floor is already below your hearing threshold. That being said the cheaper miniDSP devices do not have exceptional analog performance and you can run in to noise issues with higher sensitivity speakers and higher gain amplifiers. This forum talks a lot about SINAD but to me noise is much more important than distortion. It is pretty easy to pick out a high noise component but it is not so easy to pick out a higher distortion component (look at recent SMLS M500 THD issues as an example!). Now, whether that noise actually deteriorates your listening experience is another question but low noise equipment certainly helps ease the audiophilia nervosa.

If you can hear noise and you do not use maximum volume on your digital volume control you can certainly install some cheap line level attenuators to help maintain your SNR.

Michael

Thanks! It's only to limit the maximum volume. I will listen closer soon, but I don't hink I have any noise, so that's good.
 
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Rubberducky

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Are you implementing any boosts in your DSP? Or is the 10 dB cut just to limit max volume level?

To me the test is do you hear any noise when nothing is playing? If you cannot determine if the device is on or off from your listening position digital volume control will do no harm because the noise floor is already below your hearing threshold. That being said the cheaper miniDSP devices do not have exceptional analog performance and you can run in to noise issues with higher sensitivity speakers and higher gain amplifiers. This forum talks a lot about SINAD but to me noise is much more important than distortion. It is pretty easy to pick out a high noise component but it is not so easy to pick out a higher distortion component (look at recent SMLS M500 THD issues as an example!). Now, whether that noise actually deteriorates your listening experience is another question but low noise equipment certainly helps ease the audiophilia nervosa.

If you can hear noise and you do not use maximum volume on your digital volume control you can certainly install some cheap line level attenuators to help maintain your SNR.

Michael
I've listened, and when there is no music playing I hear some white noise until about 10cm from the speakers, any further and the noise is drowned away completely. I sit more than 2m from the speakers, so I guess this doesn't influence the sound at all then?

Line level attenuators wouldn't really work here, since the MiniDSP 2x4HD is also my DAC.
 

mdsimon2

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I've listened, and when there is no music playing I hear some white noise until about 10cm from the speakers, any further and the noise is drowned away completely. I sit more than 2m from the speakers, so I guess this doesn't influence the sound at all then?

Line level attenuators wouldn't really work here, since the MiniDSP 2x4HD is also my DAC.

The performance of the 2X4HD DAC is dominated by analog noise. When the digital volume control of the 2X4HD attenuates the main signal it will NOT attenuate the dominant analog noise. That is really the only concern with a modern device with a 32 bit digital volume control so if you cannot hear the noise I have a hard believing it will influence the sound in any appreciable way.

You can still use like line level attenuators as shown in the link below.

https://www.parts-express.com/Harri...zHiA4S8IoB_TfoNwTdayqqmJNmZ6rechoCfk8QAvD_BwE

They come in different attenuation values. Unlike digital volume control these will attenuate the main signal and noise so that you can have more SNR out of the 2X4HD. The only issue with a line level attenuator is that you are giving up DAC output level, I personally find that I like to have some extra level on tap to help compensate for recordings with a lower overall volume level.

EDIT: If it wasn't obvious the line level attenuators go AFTER the DAC (between the DAC and amplifier).

Michael
 
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mdsimon2

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Thought it might be good to add some numbers to the discussion. The 2X4HD has a specified dynamic range of 103 dB, I've measured it at 96 dB with a Motu M4 audio interface, the difference is likely due to noise from the Motu ADC, so let's use the 103 dB as that is probably pretty close to reality.

The 2X4HD has a full scale output voltage of 2 V. This implies a residual noise level of 2 x 10^(-103/20) = 14.2 uV which will always be present at the DAC output. If you attenuate by 10 dB digitally you reduce the full scale output voltage to 2 x 10^(-10/20) = 0.63 V but the noise level remains 14.2 uV. As expected the dynamic range has now decreased by 10 dB, 20 x log(0.63 / 14.2 x 10^-6) = 93 dB.

Now let's look at the case where you operate the 2X4HD without any digital attenuation and instead attenuate by 10 dB using a line level attenuator. In this case at the DAC output you have a full scale output voltage of 2 V and a noise level of 14.2 uV. The line level attenuator will attenuate the main signal to 2 x 10^(-10/20) = 0.63 V AND the noise level to 14.2 x 10^(-10/20) = 4.5 uV. In this case your dynamic range remains 103 dB, 20*log(0.63 / 4.5 x 10^-6) = 103 dB. The trade off of course is that the maximum voltage at the amplifier input is now 0.63 V and depending on amplifier input sensitivity you may no longer be able to drive the amplifier to full power. That being said the reduction in maximum amplifier power output is of no concern if you do not need full amplifier power output to achieve your desired volume level.

Michael
 
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Rubberducky

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Thought it might be good to add some numbers to the discussion. The 2X4HD has a specified dynamic range of 103 dB, I've measured it at 96 dB with a Motu M4 audio interface, the difference is likely due to noise from the Motu ADC, so let's use the 103 dB as that is probably pretty close to reality.

The 2X4HD has a full scale output voltage of 2 V. This implies a residual noise level of 2 x 10^(-103/20) = 14.2 uV which will always be present at the DAC output. If you attenuate by 10 dB digitally you reduce the full scale output voltage to 2 x 10^(-10/20) = 0.63 V but the noise level remains 14.2 uV. As expected the dynamic range has now decreased by 10 dB, 20 x log(0.63 / 14.2 x 10^-6) = 93 dB.

Now let's look at the case where you operate the 2X4HD without any digital attenuation and instead attenuate by 10 dB using a line level attenuator. In this case at the DAC output you have a full scale output voltage of 2 V and a noise level of 14.2 uV. The line level attenuator will attenuate the main signal to 2 x 10^(-10/20) = 0.63 V AND the noise level to 14.2 x 10^(-10/20) = 4.5 uV. In this case your dynamic range remains 103 dB, 20*log(0.63 / 4.5 x 10^-6) = 103 dB. The trade off of course is that the maximum voltage at the amplifier input is now 0.63 V and depending on amplifier input sensitivity you may no longer be able to drive the amplifier to full power. That being said the reduction in maximum amplifier power output is of no concern if you do not need full amplifier power output to achieve your desired volume level.

Michael

Allright! Super helpful, thank you!
 
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