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Currawong
Fukuoka, Japan
Posts 1
Joined on 08-17-2012
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Post #:
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12
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Post ID:
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18529
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Reply to:
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18182
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Experiments with computers as a source and getting good results from various DACs
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I saw this topic and it prompted me to register and reply, rather than just read, which I've been doing on and off for years now.
While I would love to have the time, space and patience for a vinyl rig, it is not going to happen, and, since quite a bit of my work is in front of my computer, I explored getting the most out of it as the transport. Just as there are a myriad of details in a vinyl system, so too are there in a computer system. Quite a few have been made redundant by the availability of better electronics, such as more recent async USB receivers, but despite that, I still find the playback software sounds different! It is crazy.
Some years ago I bought a DAC from an interesting Chinese man who makes old-school high-end equipment with heavily regulated power supplies, all discrete circuits and no negative feedback in the design. The DAC only had an S/PDIF input and was sensitive to transport quality, despite his unique effort at utilising, of all things, DSP found commonly on industrial network cards as an asynchronous computer to handle the digital signals. As time went on, he, at his customer's request, explored USB input, mostly in his cheaper DACs, as, initially, he refused to add anything at all to his reference DAC that might degrade the sound quality. He even refused my request to add an optical input so I had to buy a converter to use it with my computer!
The converter died, and I was left without my main source of enjoyment. Impulse-buying a cheap Onkyo-rebadged Philips SACD player, I didn't feel the sound was as good. I was learning my first lesson about digital transports with this experience.
Further down the line, I bought an Audiophilleo 1 USB to S/PDIF converter. The manufacturer claims that it has 1 or 2 picoseconds of jitter, only. I found someone with sufficient equipment to measure it and the result was in femtoseconds! However, despite the awesome credentials of the unit, the treble sounded a bit harsh. It uses the computer's power to run, so I thought I'd try an isolated power supply. I ended up buying a USB hub from a company called Vaunix that makes signal generators. The hub is designed to be used with their equipment, isolating and improving the power supply to equipment. This fixed the issue with the treble! Not much later, Audiophilleo came out with the Pure Power upgrade that uses a special power supply for the output half of the circuit. Correlating with what the maker of my DAC said, it seems that even if a device is very low in either of the two types of jitter, it still has to have a good S/PDIF output. Josh of Sonicweld made an interesting point that the S/PDIF output can be likened to an analogue device playing a square wave. The capabilities of that are important, independent of jitter, to the performance of the digital output of a converter, alongside the necessity of all the components having the same (characteristic) impedance. If they don't, the result will be reflections along the cable that disturb the signal. This can be easily seen on a scope.
Recently, partly out of curiosity and partly out of self-indulgence, I bought a Calyx DAC, which is totally opposite in philosophy to my main DAC. No huge power supply, no R2R DAC chips, OPAMP output stage instead of discrete component and USB input as the primary source of both power and digital music. Forum comments in various areas suggested that its USB input was better than its coax input.
Contrast the innards of both DACs. The first picture is from the manufacturer's site and the second from 6moons, since they insist on taking apart the stuff they review. The third is an old Parasound DAC1600HD, which was built with a similar philosophy to the first DAC and which I think has the most natural instrument reproduction of all three, likely due to the old PCM63K chips present.
(Sorry, but for some reason I cannot upload images, so I've put links instead.)
http://www.audio-gd.com/Pro/dac/RE7.1/RE7.115.JPG
http://www.6moons.com/audioreviews/calyx3/open2.jpg
http://csbd.org/~danchow/Parasound_DAC1600HD/Parasound_DAC1600HD_open_10.png
Though I'm very pleased with the sound from my main DAC, along with the Audiphilleo + Pure Power and Vaunix hub etc., due to all the components involved, it doesn't sound good until it has warmed up for a couple of hours. Due to the cost of power here in Japan, as well as the need to cut down on usage now almost all nuclear stations have been shut down, I can't just leave it on all day and have to switch it on when I listen, which isn't as good. My hope was that I could get good results out of the Calyx, either from its USB or using the Audiophilleo.
Unfortunately the USB input results in a sound that is rather "flat" and un-musical. The Calyx power supply improves things somewhat and the Vaunix more so, but the best results were with the Audiphilleo and Pure Power. Now I had something akin to my Reference 7.1 without the power bill but with music sounding alive and beautiful -- at least as much as it can without emptying one's wallet into the pockets of one of the various companies that make discrete resistor ladder DACs. Unfortunately those are out of my budget. Maybe one day I'll have to stop being lazy and just build one of my own, or work harder.
So though I agree computer playback can be a clusterfuck, for me it would be as much a confusion for me to, say, switch to vinyl and have to go through the motions of learning everything from scratch and dealing with a bunch of different variables.
 manisandher wrote: | Here's a computer playback approach that I though people might be interested in. In many ways, it's pretty much the leading edge of computer playback as far as I know.
The idea here is to isolate the DAC as much as possible from the PC. All the audio processing is performed in the software player which sits in a 'powerful' and potentially mechanically/electromagnetically noisy PC. The output of the software player is streamed asynchronously via LAN to an ultra-low footprint computer running Linux. The DAC is connected directly to the Linux computer. In my setup, I have a noisy PC sitting in my basement, controlled from my desktop PC using Remote Desktop.
There are a number of challenges in using this approach, not least of which are the small number of Linux drivers available. This limits the DAC choice massively. From my own experience, RME and Dice drivers work fine. Oh and not everyone is comfortable with Linux. I'm certainly not and commissioned a developer to put the necessary Linux OS onto a bootable USB stick for me.
The results are interesting. There is a clarity that I hear that I find very hard to replicate with most PC-direct-to-DAC connections. And the hardware isn't expensive - the Linux computer and necessary OS can come in under the $500 mark.
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I think this is definitely the way to go. I have a pair of very sensitive in-ear monitors a friend lent me to try. Being highly sensitive, it is easy to hear the computer noise through USB-connected devices. I was listening through a very inexpensive but pleasant-sounding DAC/amp and could hear chirps as the computer it was connected to loaded the tracks from an external SSD drive.
Though it is limited to 96k (not necessarily a bad thing as higher res files arguably have no benefit and likely detriment) it is possible to stream with an iPad, which can connect to many USB DACs using the camera connection kit. Some people are fond of modifying Squeezeboxes for this reason. Similarly, it makes a lot more sense to me now why Linn has gone in the direction of network streaming.
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