Tuesday, February 08, 2011

Still Evangelizing


Now as ubiquitous as John Boehner's smoking habits, high def TV is still alive and kicking - and growing like July crabgrass. To us audio geeks, we know what high def means; it means high sampling rates and more bits per second. If the high rez sampling rate works for TV, just think of what it can do for music.


The problem confronting audiophiles with 96K-192K, lets just call it high rez, is not finding high definition music, but playing it back properly. If the comparison to high def TV is in tact, then 192K should sound significantly better than 44,1. Alas, in most cases it does not and for some 'philes out there, they can hardly tell the difference. So, back to my original theory: there must be a problem with playback.

As you can clearly see from my CyberServer videos, the PC is the problem. Being a computer jock, I know a little about PCs and USB. The block input / output that USB uses requires a pre-fetch of data blocks to be placed in computer memory, where, it is clobbered to death by other high speed clocks on the mother board and graphics card. Computer memory is not a good place for Oscar Petersen. Its really bad, if Oscar is at 192K. Using your computer for high rez playback is like watching high def TV on the SONY Trinitron: it just was not made for it.

They still can't convince me that the standard USB 2.0 drivers are adequate for high end audio and attaching a well made music "streamer" is the end all. The standard USB drivers are not fast enough for 192K (they were never meant to stream music, you see? ) and can barely do 96K. If audiophiles used DACs like the Matrix mini that display the sampling rate, they would find that most DACs, find so much jitter in the 96K signal that they down sample it to 48K. If the Audio gd DACs find ka ka in the signal, they just shut off, refusing the play the mess. The only way to get 192K and 96K reliably out of a PC is to replace the drivers a la Musiland or M2Tech. While they make a world a difference, you still have the block input / output - pre-fetch problem described earlier.

One easy solution to the USB problem is to get a computer with what is called "streaming" I/O (I/O stands for input / output). Streaming I/O reads a byte - writes a byte. No memory to muck up the sound, no blocks with their choppy latency that translates into jitter. While fairly primitive, streaming I/O is ideal for digital playback. The best operating systems to make use of the streaming I/O are the Unix / Linux brands. Here, a computer programmer can open a music file and specify this somewhat primitive I/O mechanism for the pushing the music file down the stream.

The next fly in the high rez ointment, is latency. Since the computer is not really meant for high speed streaming of anything, latency abounds. The DAC sees latency as jitter, and although the asynchronous USB drivers help, they are not as fast as they need to be so latency prevails. You have to cut latency anywhere you can: on the I/O bus, which carries the digital music, to the hard drive. The hard drive is slowest of the bunch and any increase in I/O speed from the disk yields an appreciable improvement. A solid state drive is about 40% to 50% faster that a conventional hard drive with a motor. Its one drawback is that it is expensive. Like a sports car, you pay for speed.

When you put this all together, a Linux operating system with streaming I/O and a solid state drive, you get CyberServer. I cannot tell you how happy we were to see Byrston trying this same idea out with their new media server. One thing though, the Bryston costs over $2K price tag - although it uses a terabyte. The USB thumb drive that they use, in our opinion, may still be a little too slow. Stick with the faster solid state ones. Ours start at $720.

All the best,
Vic

2 comments:

Pt said...

Hello,I am not technically bacgrounded in this topic so I may be wrong in the following reasoning but: wouldn't it be possible to load a music in the RAM before playing it. So the latency would be very minimal. Also, I don't get completely the "buffer" story but isn't this a possible solution for jitter problems.
All in all, you already got me interested in the argument. There is a good probability that I will try just what you describe: Linux+SSD+I/O stremaing.

Vic Trola said...

The issue is that a computer's RAM is the worst place for music. It is surrounded by EMI that clobbers it like gamma rays on the skin. Ouch!