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Use of Preamp versus Digital Volume from Computer

Has anyone done a direct comparison of using a high quality preamp in a computer audio setup to control volume from DAC to the amp, versus going straight from DAC to amp and using the computer to attenuate volume via the playback software?

Not necessarily looking for speculation or general opinion as there's plenty of that to go around, just feedback from those that have compared or have true knowledge of the pros/cons.

I've had 3 different computers and 4 different DACs over the past year or so, where I've used Itunes to control volume (feeding an Empirical Audio Turbo-3). Nothing really for me to complain about as far as sound. I've heard that the Turbo-3 (by way of converting 16 bit to 24 bit) actually helps the quality of the digital volume attenuation.

My system is fairly resolving with the Turbo-3, Isabellina DAC, modded Rogue Stereo 90 tube amp and Living Voice IBX-R2 speakers all fed via either an IMac or Macbook from Itunes.

It's a stupid question for me to pose personally since it's a bit of "if it's not broken, don't fix it". My system sounds fine to me for redbook playback. But curious how much alteration the digital volume control is doing to the digital feed from the computer to the DAC (or in my case the Turbo-3).

Thanks,

Marc
mb9061
4 responses Add your response
herman
2,253 posts
 
I'm using a program called Pure Vinyl on my Mac which uses 64 bit processing and a digital volume control. The Mac is hooked up to an RME Fireface 400 via firewire and I modified the outputs to bypass the opamps so I'm going straight off of the DACs to my power amps. It sounds incredible.

You are right that the higher number of bits gives you better results but that has to be done in the software before the attenuation, not after in hardware. I think you would be pleasantly surprised if you tried the Pure Vinyl. They have a free demo. You can use iTunes as the front end and there is a little window with the Pure Vinyl controls that floats on top of iTunes for volume control and moving through the playlist.
mb9061 OP
137 posts
 
Thanks Herman.

I'd heard some time back that Itunes versions 7 and up had dithered volume control that was quite good versus truncated 16 bit volume that was found in earlier versions (Benchmark's website has a write-up on it for example).

I can't tell any loss in sound quality with using Itunes to control the volume and most my listening is done with the volume at 10-30% of max, controlled via an IPod Touch with the remote app. But I see lots of people saying to set it at a full 100% and go with analog attenuation (which I tried via several different integrated amps and didn't really care for).
aljordan
46 posts
 
Hi,

The only time when I noticed a sound quality difference between a digital and analog volume control was when I had to attenuate a large amount via the digital volume control. At the time, the tests were done using a Lynx Studio 2B sound card. If you are attenuating a large amount via a digital volume control on 16 bit material, you are bound to lose some dynamics. However, (I think as the previous poster commented) there are software packages that convert to 64 bit internal math, and with them you can generally get very good sound with little loss of dynamics using digital attenuation.

I think a more important question is if your DAC drives your amplifier well. If so, then having a preamp in the mix might do more harm than good. In my case, I have amplifiers with fairly low input impedance, and I find a high quality preamplifier improves dynamics and response at the frequency extremes.

Alan
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