# Digital 2 channel Dirac system questions



## Brad.Scott (Apr 28, 2015)

Hi I'm new to this form.
I'll be setting several Dirac systems in a home addition over the next year.
One is a 2.2 channel primarily digital system. I'm looking at 2 possibilities.

The first is is a Minidsp DDRC-22DA digital pre-amp DAC with 2 channel Dirac (96/24) feeding 2 Crown XTi 1002 amps. The DSP in the Crown amps will cross over between the 2 channels to a Main speaker and Sub (located in close proximity) and the time delays will align the speaker/sub as a single channel (one amp for each channel). Dirac will see the speaker/sub as one channel.

The second option is similar. A Minidsp DDRC-22D (digital only 2 channel Dirac) will feed an Emotiva Stealth DC-1 DAC preamp which will feed the 2 crown amps.

Has anyone used the DDRC-22DA as a digital preamp? How does the quality of the DAC compare to the DC-1?
The Minidsp uses a digital volume control while Emotiva uses an analog one. Any advantage to one over the other? 

Thanks, Brad


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## Lumen (May 17, 2014)

Hi! You're really patient! Are you still interested in an answer, or did you find one somewhere else? If you like, I can try and move this post to a different forum for you to improve the chances of an answer.


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## Brad.Scott (Apr 28, 2015)

yes, I'm still interested. Thanks


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## Lumen (May 17, 2014)

You're welcome, Brad. I've raised awareness of your post with the staff, so someone should be getting back to your soon. In the meantime, I can try to answer at least one of your questions on a superficial level. Comparing chip-level DAC's is like comparing apples once they've already been baked into a pie. You can't separate their flavor for fair comparison. Component-level DAC's today are so advanced that distinctions between chips are smeared. It's how they're implemented that can makes a (small) difference. Larger differences between comp-level DAC's can be attributed to their analog output stages and filtering.

By the same token, it would be a fair test to try and hear differences between a digital or analog volume control _on the same audio component._ There are just too many variables in the signal chain to draw valid conclusions by comparing a digital control in one component with an analog control in another. Either should suffice if competently designed (which sometimes boils down to brand reputation, like ALPS). Traditional thinking has it that digital controls are handicapped through the way they truncate bits to lower volume, thus throwing away subtle and vital clues that allow astonishing sound stage and imaging (SS&I). But there are ways around this hurdle. Here's an excerpt from an article in Soundstage that explains it better than I (emphasis is mine):

_"....there is more to digital volume control than truncating bits. Just lopping off unneeded bits is a very crude way of adjusting the scale of a digital signal. As the volume is reduced, the use of a proper dithering algorithm is necessary, not to introduce highly unpleasant quantization distortion into the reconstructed signal. *Some of these algorithms are better than others, and the results can be audible.*

Of course, the digital signal must eventually be translated into the analog domain, and that is where the understanding of digital vs. analog volume controls becomes more complicated. The crucial parameter is dynamic range, which is the relationship between the peak amplitude of the audio signal and the underlying noise floor of the circuit. When a DAC with a fixed output is followed by a passive attenuator -- e.g., a potentiometer -- the peak signal and noise are reduced by the same amount, so that the dynamic range remains constant. With a digital volume control, the peak signal level is reduced, but the underlying noise remains the same -- consequently, there is a reduction in dynamic range. *The degree to which this loss of dynamic range is a problem depends on the inherent noise level of the DAC*."_

Hope some of that helps :wave:


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## Brad.Scott (Apr 28, 2015)

Thanks for your quick reply. Both Emotiva and Minidsp have good reputations on sound quality and are the only companies offering Dirac at relatively low prices. I bought an XMC-1 for another system in the addition and it will be feeding the 2.2 system for analog sources (which it will down mix to 2 channel digital).


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## AudiocRaver (Jun 6, 2012)

Brad.Scott said:


> Hi I'm new to this form.
> I'll be setting several Dirac systems in a home addition over the next year.
> One is a 2.2 channel primarily digital system. I'm looking at 2 possibilities.
> 
> ...


I have not heard the analog out of the DDRC-22DA or the DC-1, so can't help you there. The DDRC-22DA digital volume control is implemented in the 32-bit processing realm of the DSP and works in 1/2 dB steps, where the DC-1 has a digitally controlled resistive ladder with 1/4 dB steps. The DDRC-22DA itself does not have a gain readout, but miniDSP is planning to update the android and ipad control apps so the gain control in them has a gain readout - not quite as _convenient_ as the DC-1's nice front-panel readout. The difference in resolution is not an issue, 1 dB steps are fine enough to get you to the volume you want. If -2 is too loud and -2.5 is too soft, you were born in the wrong body, should have been a bat or a dolphin.:bigsmile: Neither design will add noise or distortion.


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## AudiocRaver (Jun 6, 2012)

BlueRockinLou said:


> _"....there is more to digital volume control than truncating bits. Just lopping off unneeded bits is a very crude way of adjusting the scale of a digital signal. As the volume is reduced, the use of a proper dithering algorithm is necessary, not to introduce highly unpleasant quantization distortion into the reconstructed signal. *Some of these algorithms are better than others, and the results can be audible.*
> 
> Of course, the digital signal must eventually be translated into the analog domain, and that is where the understanding of digital vs. analog volume controls becomes more complicated. The crucial parameter is dynamic range, which is the relationship between the peak amplitude of the audio signal and the underlying noise floor of the circuit. When a DAC with a fixed output is followed by a passive attenuator -- e.g., a potentiometer -- the peak signal and noise are reduced by the same amount, so that the dynamic range remains constant. With a digital volume control, the peak signal level is reduced, but the underlying noise remains the same -- consequently, there is a reduction in dynamic range. *The degree to which this loss of dynamic range is a problem depends on the inherent noise level of the DAC*."_


*No* reputable designer would control gain by dropping bits.

It is a multiplication function, and in a processor like the DDRC-88A it is mixed in with thousands of other types of DSP math operations done in 32-bit precision math, so it has 256x better resolution than the 24-bit audio being processed, in terms of creating or adding distortion. Yes, the signal to noise ratio SNR decreases as the volume is reduced, but when you consider that the volume setting that most listeners use on their DAC is probably never lower than 20 dB from their normal listening level, if that, the SNR is reduced from, say, 125 dB - about the practical SNR limit for any DAC regardless of bit depth, unless one resorts to cryogenics - to 105 dB, still an excellent number. If that number was getting reduced to 80 dB or less, then there might be reason for concern.

Now, one might _feel_ better about the analog ladder's better spec emotionally, or just want it because they like the idea of it, and that is perfectly fine, but expecting to ever _hear_ a difference (noise &/or distortion) is a big stretch, unless I am missing something obvious. A lot of us buy components that operate 10x or 100x or whatever better than what we are likely to ever be able to hear, just because we can and we like the idea of it - and why not? No harm done if we can afford it.

In this case, I like the idea of the resistive ladder DAC, but do not see there being an audible difference under even extreme conditions.


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## Brad.Scott (Apr 28, 2015)

Thank you, very helpful. I'll probably go with the Minidsp DAC preamp.


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