Cambridge Audio DacMagic Plus digital volumen control - diyAudio
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Old 17th November 2011, 03:59 PM   #1
pof@ is offline pof@  Denmark
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Default Cambridge Audio DacMagic Plus digital volumen control

Iím building a system like this:

Squeezebox Ė> PC for FIR filter -> 2 x DAC -> 2 x Power amp -> 4 x drivers

I hope to end up with some "high-end" sound.

If I would use the volume control from the Squeezebox it would kill some of the dynamics. The best way might be to have a multi channel analogue preamp between DACís and power amps but Cambridge Audio is launching a DAC with digital volume control.

DacMagic Plus Digital to Analogue converter

Would this be a good thing to put in between Squeezebox and PC digital in and digital out? I donít know how the volume control is done, but if 16 bit is converted to 24 bit and then attenuated the loss of dynamics would be acceptable?
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Old 18th November 2011, 12:46 AM   #2
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The DAC volume control is going to be a 24 bit volume control since everything coming in is converted to 24 bit anyway.

The Squeezebox family all output 24 bit streams too, regardless of input format, and their volume controls operate in 24 bit.

Since you need the volume of both your DACs to be in sync and the Cambridge doesn't offer any way of remotely setting the volume then your options are to control the volume at a single point digitally in the Squeezebox, at two points digitally in your DSP crossover, or in analogue post-DAC. This means you have to get 4 very accurate tracking attenuators though, and this may outweigh any advantage of keeping the signal unattenuated in the digital domain.

I don't think the new Cambridge model is going to do anything useful for you unless you put an elastic band between the two volume pots!
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Old 18th November 2011, 01:12 AM   #3
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The web page for the DACmagic you linked to says this:

Asynchronous USB transfer for very low jitter

You won't get high end sound if you have two of these DACs in your system because each one will have its own idea of what the playback frequency is. That means your HF and LF will gradually drift out of phase with each other, with no limit to the phase errors over time.

You'll need to find a DAC which allows the PC to be the clock master to allow your digital XO scheme to work.
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Old 18th November 2011, 09:28 PM   #4
pof@ is offline pof@  Denmark
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@paulster: I would insert the Dacmagic Plus between Squeezebox and PC.

@abraxalito: My soundcard is RME HDSPe AIO and I would use the SP/DIF I/O

But I found a problem in my idea. Spec says Audio output up-sampling: Fixed 24-bit/384kHz and my soundcard does only support up to 192 kHz.

But the Dacmagic Plus would have solved a problem with different sample rates and bits. But because of the 384 kHz I have to drop that idea :O(
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Old 19th November 2011, 06:21 AM   #5
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Quote:
Originally Posted by pof@ View Post
@paulster: I would insert the Dacmagic Plus between Squeezebox and PC.


But I found a problem in my idea. Spec says Audio output up-sampling: Fixed 24-bit/384kHz and my soundcard does only support up to 192 kHz.

But the Dacmagic Plus would have solved a problem with different sample rates and bits. But because of the 384 kHz I have to drop that idea :O(

Hi Pof

If I understand You correctly, C.A. are speaking about the internal working way of its converters ( 24/384 re-sampling ) and it is independent of the digital output of your sound card .
So go on, if You decide to buy a dacmagic plus ,and tell Us how sound this little beast ( I suppose it will be tuneable like old one....)

ciao
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Old 19th November 2011, 09:16 AM   #6
pof@ is offline pof@  Denmark
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@bicefalo
I wanted to feed the PC soundcard from the Dacmagic digitally.

But I misunderstand the specifications, "Audio output up-sampling: Fixed 24-bit/384kHz" is only referring to what the internal DAC is fed to convert to the analogue output.

Digital outputs are pass-through only; there is no upsampling or any other modification done to the LPCM input signal. I was hoping for a true digital preamp

So I have to do the attenuation in the PC if there is no other suggestions to solve this. The analogue attenuation after the DAC's is another project for later.

Last edited by pof@; 19th November 2011 at 09:20 AM.
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Old 19th November 2011, 06:17 PM   #7
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Why don't you do the attenuation in the Squeezebox, which is already set up for it, offers remote control of the volume, and operates in a 24-bit domain anyway? Even if the Cambridge had a digital out that was affected by the volume control it wouldn't achieve any more than the Squeezebox does already since it too implements a 24-bit digital volume control.
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Old 19th November 2011, 06:47 PM   #8
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Default DacMagic Digital Preamp Mode

Quote:
Originally Posted by paulster View Post
the Cambridge doesn't offer any way of remotely setting the volume then your options are to control the volume at a single point digitally in the Squeezebox, at two points digitally in your DSP crossover, or in analogue post-DAC. This means you have to get 4 very accurate tracking attenuators though, and this may outweigh any advantage of keeping the signal unattenuated in the digital domain.
Just a quick note on the DacMagic Plus digital VC- it comes out of the box set in "digital preamp mode" although there is a very simple process to put it in fixed output mode. Power down (hard) --> Hold VC down while powering the DacMagic Plus back up. Voila! Although this doesn't address the other issues mentioned in the thread (i.e. multiple asynchronous DACs), it does bypass one issue.
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Old 20th November 2011, 10:49 AM   #9
pof@ is offline pof@  Denmark
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Quote:
Originally Posted by paulster View Post
Why don't you do the attenuation in the Squeezebox, which is already set up for it, offers remote control of the volume, and operates in a 24-bit domain anyway? Even if the Cambridge had a digital out that was affected by the volume control it wouldn't achieve any more than the Squeezebox does already since it too implements a 24-bit digital volume control.
I think you're correct. I was under the impression that the Squeezebox attenuation was badly made but based on your comment I did a search on www. Couldn't find anything except that analogue attenuation is better.

RightMark Audio Analyzer test: comparison

Digital Volume Control and SNR - SqueezeboxWiki
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