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 Post subject: SHM-CD
PostPosted: 16 Oct 2014, 05:22 
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Joined: 14 Feb 2010, 13:13
Posts: 663
Location: Lisbon, Portugal
Hi!

I wonder what is your opinion on these?

Do you own some or have heard?

They seem to be popular in Japan, and getting some fans here in Europe.

Cheers,
Miguel


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 Post subject: Re: SHM-CD
PostPosted: 19 Oct 2014, 11:34 
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Joined: 06 Apr 2009, 10:08
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Location: US Pacific Northwest
This is one of those technology improvements that is out beyond the "knee of the curve" as we say in Engineering. Such changes typically yield very small improvements in performance per design change dollar. The SHM-CD is one in which the clear layer of the disc has been replaced with a harder, lower optical loss, polycarbonate layer. The net effect is that this reduces the origination Bit Error Rate (BER) when initially reading the data on the disc.

Now normally one might say that this is a good thing; but there is more to reading a CD than just getting bits off a disc. When reading a CD, the recording substrate is moving at a significant velocity under the read head. As such, data comes off in a serial manner flowing back into buffers where the individual data words are are separated, parallelized, and stored. Now there is a small but non-zero error rate in reading the disc which means that not all of these data words match what is really on the disc. As such, the hardware runs what is called EDAC (Error Detection and Correction) algorithms to "repair" words which are in error. This is possible due to two overlapping phenomenon. The first is a BER which is low enough that it it VERY rare to see more than one bit error in a word. The second is that the pattern of the encoding is such that a bit in error can be readily identified. This means that the EDAC can correct virtually all the read bit errors.

Now enter the SHM-CD. Due to the way that discs are read today, there will be virtually no difference in the resulting read between standard CDs and the SHM variety. However, due to the much harder polycarbonate layer, it is possible that the discs will be more resistant to damage (even microscopic scratches can affect BER) and will last longer. But that is mostly speculation at this point.

The real opportunity that this may provide at this point is an an enabling technology to allow a more densely written disc using the same read laser, thus enabling higher bit depth or sample rate. Now this is already possible with some other similar technologies (DVD being the most common) but these all require a different laser. Only time will tell if this is something that really takes off. It will mostly depend if the standard becomes an accepted part of the commercial CD standard set and how it compares in manufacturing cost to traditional CDs.

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It's all about the Glass!
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 Post subject: Re: SHM-CD
PostPosted: 19 Oct 2014, 14:34 
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Joined: 14 Feb 2010, 13:13
Posts: 663
Location: Lisbon, Portugal
Excellent Matt!

I really appreciate your words.

I do have one XRCD24 and also one SHM-CD.

The XRCD24 is Fritz Reiner / Chicago Symphony Orchestra - Strauss Waltzes, and the sound is OK, maybe not a good comparision because it was recorded in late 50´s.

The SHM-CD is Frank Sinatra - Nothing but the best, and it sounds very well with lots of detail, with natural sound. But the audio is greatly compressed, far away from the loudness war we´re getting on cd´s right now. I don´t like to hear this cd that much, because instruments are all leveled and normalized, and so his voice.


Miguel


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