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How to properly volume match DACs?

bsas

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So, I am wondering how one can properly A/B test two DACs if one of them (or both) don't have any kind of volume control in the output stage. I understand the concept of using a multimeter and a signal gen to match the voltage on the DACs, but, if they don't have a way to volume control and both are going to an RCA A/B passive switch box, how to match them? Maybe two identical pre-amps before the switcher? But doesn't the preamp changes the results on that situation?

Thanks!
 

gvl

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You can do it in software on PC/Mac. Send the same input to both DACs and apply digital attenuation on each path so that the output voltage matches. Which software? Good question. I'm sure it exists. JRiver might be able to do this but I haven't tried.
 
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bsas

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Hmmm, but in that case you would be modifying the source, no? What if digital attenuation can bring loss of resolution because of data compression?
 

levimax

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So, I am wondering how one can properly A/B test two DACs if one of them (or both) don't have any kind of volume control in the output stage. I understand the concept of using a multimeter and a signal gen to match the voltage on the DACs, but, if they don't have a way to volume control and both are going to an RCA A/B passive switch box, how to match them? Maybe two identical pre-amps before the switcher? But doesn't the preamp changes the results on that situation?

Thanks!
someting like this https://www.amazon.com/Audio-Contro...K,B074Z5C94X,B01D5H8P0G,B00LBK3870,B003FPD3IS or I built my own out of a 20 K multi- turn pot and old rca cable ends
 

Blumlein 88

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Yeah do it in software. You'll need to attenuate the higher voltage source. You also could reduce the level and save the file having two files one for each DAC.
 
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bsas

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Blumlein 88

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Hmmm, but in that case you would be modifying the source, no? What if digital attenuation can bring loss of resolution because of data compression?
Depends upon the particulars. If you have to reduce one source by a large amount it might matter, but in most cases with most source files even dropping by half won't matter.
 

gvl

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Hmmm, but in that case you would be modifying the source, no? What if digital attenuation can bring loss of resolution because of data compression?

If done right the differences introduced my this method will be negligible if any, much less than that of a dual preamp you had in mind .
 
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bsas

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Yeah do it in software. You'll need to attenuate the higher voltage source. You also could reduce the level and save the file having two files one for each DAC.

I am not an expert in electronics but software development is my expertise (and my daily job) and I am pretty sure that digital attenuation can decrease signal detail because of compression (rounding number issues, not audio compression)... am I mistaken here? :(
 
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bsas

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If done right the differences introduced my this method will be negligible if any, much less than that of a dual preamp you had in mind .

Hmmm, I can see that the digital loss can be less than bad preamps loss, but isn't possible to get good preamps that will be better than the digital loss?
 

gvl

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I am not an expert in electronics but software development is my expertise (and my daily job) and I am pretty sure that digital attenuation can decrease signal detail because of compression (rounding number issues, not audio compression)... am I mistaken here? :(

It can, however if DACs are 24-bit capable and you use 16-bit source file you have a lot of headroom before you start losing bits.
 
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bsas

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It can, however if DACs are 24-bit capable and you use 16-bit source file you have a lot of headroom before you start losing bits.

That is true... Hmmm, any software recommendations? Preferably it would be great to have a software that could do that and also play on two dacs at the same time to make blind A/B even "more blind" :D
 

gvl

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That is true... Hmmm, any software recommendations? Preferably it would be great to have a software that could do that and also play on two dacs at the same time to make blind A/B even "more blind" :D

JRiver can send to two devices at the same time, but I'm not sure if you can apply different volume on each.
 

Lambda

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LCR and impedance characteristics of the signal?
This is the whole point... thy can be made impedance matched for Ghz signals.

just measure the output difference and then build a custom attenuator.
Possibly with trimmer resistor to fine tune later
 
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bsas

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This is the whole point... thy can be made impedance matched for Ghz signals.

just measure the output difference and then build a custom attenuator.
Possibly with trimmer resistor to fine tune later

Interesting, I am not an electronics expert, so, how one can "impedance match" attenuators? If one knows the impedance of the source, is there just an simple calculation so you can choose the proper resistance for the pot?
 

Kal Rubinson

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JRiver might be able to do this but I haven't tried.
River can send to two devices at the same time, but I'm not sure if you can apply different volume on each.
It can and it is simple. It also does the attenuation at the 64bit level.
 

Lambda

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how one can "impedance match" attenuators? If one knows the impedance of the source, is there just an simple calculation so you can choose the proper resistance for the pot?

Complete over kill for audio but if you want to keep the Impedance the same the same
Measure the source impedance and make an pi pad to keep the impedance the same
 
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bsas

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Any recommendation for a good RCA switcher?
 
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