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In Reply to: RE: Is there such thing as (digital) source selection and volume control in the digital domain? posted by andyr on January 25, 2015 at 00:46:01
digital volume controls work by throwing away bits.....
Follow Ups:
"digital volume controls work by throwing away bits....."
And normal analog volume controls work by throwing away signal energy.
'bout the same thing Stu. Seems like a better idea is to not over-amplify in the first place.
Rick
Care to elucidate?
Thanks,
Andy
Throw away bits and you throw away data.
"Throw away bits and you throw away data."
Depends. If there was 16 bits of data to start with and you convert it to 24 bits and then turn this down -24 dB and send the result to a 24 bit DAC you will still have 20 bits of data left, more than you started with. In other words, you will have lost no data. In the case of DACs using the SABRE chip the internal data path is 32 bits, so 24 bit audio files can be turned down a similar amount without any loss.
If the lower output from the DAC causes you to increase the volume control on your preamp then you may hear more noise out of your speakers. This depends on the gain staging of the entire playback chain. With my SABRE based DAC direct into powered speakers there is no audible noise out of my speakers even with an ear 2 inches from a tweeter when playing a quiet 24 bit track and even with the volume control turned all the way up. Normally, the volume control never gets above -5 dB (when playing some Mahler symphonies), -25 dB for harpsichord music, etc... So there is no loss of resolution, either, due to noise floor.
If you have a 16 bit DAC then any kind of digital volume control is a bad idea, because there aren't enough bits to start with. If you have a 24 or 32 bit DAC it is possible that a digital volume control may sound better than an analog one, especially if it eliminates entire stages of analog gain. The only way to tell is to listen and compare. (My DAC allows the choice of an analog volume control or a digital volume control.)
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
It depends on the bit depth and SNR of the recording and the dynamic range that the rest of the system is capable of.
These days, a lot of digital volume controls are implemented with a 32-bit word length. If the input is 16 bit, you can attenuate by 96 dB without losing anything. Even if the volume control is 24-bit, you can attenuate by 48 dB without losing anything, which is more range than any system needs.
And what about the worst case of 24-bit input into a 24-bit volume control? You're still not necessarily losing anything because the 144 dB of dynamic range at 24-bits is greater than the analog portions of the chain provide a maximum volume. Unless your system has way too much gain, the theoretical digital noise floor imposed by the volume control is below the analog noise floor. And 24-bit recordings don't have 144 db of dynamic range anyway.
So digital volume control is feasible (and miniDSP offer this option).
Have you any suggestion for source selection beween all-digital sources?
Regards,
Andy
A DEQX HDP-4 seems like the perfect option for you. Everything you need in one box, the price isn't crazy ($5500), and they can guide you through the setup and calibration process.
An other one-box option is a Trinnov MC Processor or magnitude32, which should do everything the DEQX can do but also includes a much better room optimization package. The price will be somewhere > $10k though.
A more complicated, but cheaper option is to use a standalone ADC, a digital source switch, a miniDSP nanoDIGI 2x8B into a good quality multichannel DAC like the exaSound e28. The volume control should be done in the DAC rather than the source switch.
For a digital source switch, you can use something like this:
http://www.audioauthority.com/product_details/1177A
Or you can get a pro monitor controller to do the ADC and source switching. But if you want good ADC it won't be that cheap.
But by the time you add up the cost of the ADC, source switch, miniDSP, multichannel DAC, and measurement microphone, you will probably have spent as much as you would have for the DEQX.
My problem is, my current setup is that my AKSA GK-2 hybrid preamp has 2 outputs:
#1 comes out after the main ss part of the preamp.
#2 comes out after the unity-gain tube buffer which follows the ss part.
The difference is:
* the tube output has some 'tube magic' - so ideal for mids and highs.
* but the tube softens bass transients, slightly - so bass drivers are better fed from the ss stage.
So I use output #1 (currently) to feed my bass drivers - and when I include subs, these will also be fed by output #1.
Output #2 feeds the mids & tweeters.
My reading of the HDP-4 specs suggested it can't cope with this scenario.
So, you suggested a good quality multichannel DAC like the exaSound e28. Can this be used as a substitute for the output DACs on the miniDSP? (It has 8 channels, so is exactly what I need ... if it is better than the intrinsic miniDSP DACs.)
Regards,
Andy
I had thought you wanted to replace the pre-amp. You mentioned wanting a 3-way active digital crossover, digital source switching, and volume control. That is the DEQX in a nutshell. But if you want to keep the current pre-amp, then I have no idea how it would fit in.
I would not recommend using the miniDSP as an ADC or a DAC for the main channels of any audiophile system. I would use it as a DAC for the subwoofer, but that's it. That's why I suggested using the digital-only nanoDIGI 2x8 with a good multichannel DAC. I don't have any personal experience with the exaSound, but it is well regarded.
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