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How to properly volume match DACs?

JSmith

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What if digital attenuation can bring loss of resolution because of data compression?
Digital attenuation is just a multiplication of all the data samples by a fixed coefficient.



JSmith
 
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bsas

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Digital attenuation is just a multiplication of all the data samples by a fixed coefficient.



JSmith

PCM data is composed by integer numbers. If you multiply for a fraction you can have rounding errors.
 

gvl

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PCM data is composed by integer numbers. If you multiply for a fraction you can have rounding errors.

24 bits is enough resolution to basically make it a non issue.
 
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bsas

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24 bits is enough resolution to basically make it a non issue.

Fair enough, but, that is if you are getting an 16bit source and up-sampling to 24bit to avoid the rounding issues. But, what if you are dealing with an already 24bit (or 32bit) source? I know it is very marginal, but the imperfections introduced by a good preamp supposed to be marginal as well, right? At the end of the day it if is the only way, fine. I was just wondering if there was another "analog" way that would be better (or maybe industry standard) since I believe a lot of people here does A/B tests :D
 

gvl

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For a couple dB of attenuation you need to equalize the DACs the losses even if you start with 24bts will be negligible. If you add an active preamp you’re usually adding significantly more harmonic distortion in comparison.
 
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bsas

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OK, I am convinced to try the digital attenuation. I was able to play in sync with two different DACs on Jriver (using the Zone method). I was wondering if you can setup the digital attenuation on those zones (I am a newbie with Jriver and I am testing the trial version to decide to buy or not the software).
 

gvl

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@Kal Rubinson says it can be done. There’s is DSP control somewhere in settings with parametric EQ and what not, I’d start looking there.
 
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bsas

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@Kal Rubinson says it can be done. There’s is DSP control somewhere in settings with parametric EQ and what not, I’d start looking there.

Is it as simple as just setup the "Volume" of each zone to "Internal" and change the volume in the zone to match?
 

LTig

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Fair enough, but, that is if you are getting an 16bit source and up-sampling to 24bit to avoid the rounding issues. But, what if you are dealing with an already 24bit (or 32bit) source?
The level of the lowest bit of a 24 bit source is about 144 dB below maximum level. This then is the level of the rounding errors (a bit crude). So you can attenuate up to 24 dB (144 - 120) before rounding errors reach audible levels at 120 dB below maximum signal.
 

LTig

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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?
Digital attenuation can also hide flaws in a DAC. There are DACs where THD rises close to 0 DBFS which may be audible but not when running attenuated.
 
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bsas

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OK, so, I've got two RCA passive attenuators (basically boxes with 20k pots) and one RCA A/B passive switcher. I hocked two different DACs to my PC and used JRiver to play on both at the same time the same files. I first made one big 440Hz tone file and played on both and used my multimeter on V(AC) to equalize both (both played on about 1.8V). Plugged both to the A/B box and the box to my L50 headphone amp. Switched back and forward, change DACs...

Conclusion: I just don't have enough "golden" ear to hear a difference :(... They sound so similar that is kind of splitting hairs to find anything to pay attention to. And almost any combination of two DACs sound extremely similar. I feel that I am doing something wrong...

Do you guys have any specific music recommendation that let the differences more obvious?
 

levimax

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OK, so, I've got two RCA passive attenuators (basically boxes with 20k pots) and one RCA A/B passive switcher. I hocked two different DACs to my PC and used JRiver to play on both at the same time the same files. I first made one big 440Hz tone file and played on both and used my multimeter on V(AC) to equalize both (both played on about 1.8V). Plugged both to the A/B box and the box to my L50 headphone amp. Switched back and forward, change DACs...

Conclusion: I just don't have enough "golden" ear to hear a difference :(... They sound so similar that is kind of splitting hairs to find anything to pay attention to. And almost any combination of two DACs sound extremely similar. I feel that I am doing something wrong...

Do you guys have any specific music recommendation that let the differences more obvious?
I think you are doing it right. I had the same experience with 2 different amps which I could not tell apart level matched and blind. Lots of people read about level matched blind testing but experiencing it for yourself is powerful.
 
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bsas

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I think you are doing it right. I had the same experience with 2 different amps which I could not tell apart level matched and blind. Lots of people read about level matched blind testing but experiencing it for yourself is powerful.

Interesting... I am kind of hearing "some" difference after A LOT of back and forward and I am starting to imagine if my brain is just making up a difference now :(

I am comparing extremely good measurement DACs (like the D50s and the E50) vs an R2R DAC that measures "OK for a R2R" (Ares II) and cheaper DACs like a DragonFly Black, the Liquid Spark and the ancient (first good DAC I bought) Audioengine D1... I "can" hear "some" difference but let's be honest, it is close to nothing!
 

Chrispy

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differences.jpg
 
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bsas

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Now, seriously. I am looking for suggestion for songs that anyone can promise me I will hear a monster difference, so at least I can believe that there is any difference whatsoever... from modern DACs (like the new E50) to my trusty old D1 that cannot even play more than 96Khz... :p
 
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