In a modern properly designed player, transports should make no difference to the sound. Here is an example of why this is the case:
Take any cheapo transport for $10, read the data from the CD/DVD/SACD into RAM. Use the cleanest possible clock reference and read the data from this RAM for further processing. Hence you get perfect data with the cleanest possible clock.
An Ipod Nano has this type of "transport" or non-transport. Of course other design elements of the Nano makes it non-reference such as the compression of the data and the inexpensive output processing. But it does have a perfect "transport".
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Questions are: 1.) is adaptive error correction good enough. 2.) what influence does mechanical vibration have on (1.) and on the overall performance of the player/transport. I wish I could answer these... I cannot, but I too have heard significant and very meaningful differences among transports.
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Answers:
1. Error correction is designed to fix bit errors. These are gross errors. Ever drive your car thru a bump and your CD player skips? Error correction is designed (together with buffering) to fix these types of problems. If you plan to listen to your music while thumping the player with a hammer, then I would be concerned about how good the error correction is.
2. Mechanical vibration is answered in (1) above.
The transport has no effect on the signal data if it is read out to a storage device such as RAM prior to further processing.
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I am not referring to any specific CD/DVD player. In our hypothetical CD/DVD player, the entire song can be uploaded to RAM (i.e. computer memory). This is very inexpensive. Once the song is in RAM which is a digital circuit, it can be read out and processed by the other digital circuits of the CD/DVD player. These circuits perform error correction decoding and filtering. These are typical circuits in any CD/DVD player.
The key point here is that once the song has been uploaded to RAM, the transport is no longer part of the signal path. It is effectively non-existent. You can think of an Ipod Nano as a CD/DVD player which has the song loaded into RAM. Of course the loading of this data is performed from a PC and not a transport.
Once the digital signal has been processed by the digital circuits, this signal has to pass thru a D/A converter. The quality of the D/A converter as well as the clock which clocks the D/A converter can effect the sound quality. If the clock is sufficiently jittery, you will hear this.
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As you know any computer today can play a CD/DVD. But a CD/DVD player does not have to be as complex as a computer. A CD/DVD player does not require an operating system. However, it does have firmware, i.e. software which runs the hardware. Dont forget that all CD/DVD players are digital systems anyway so they already have RAM memory. If properly designed, a CD/DVD player can offload all data into RAM prior to playing the music hence relegating the responsibility of the transport to merely a temporary storage for the music. Furthermore once the data has been offloaded into the RAM buffer, the transport no longer has an effect on the quality of music. Just think of the CD/DVD disc as inexpensive storage and the transport as a means of transfering the data on the CD/DVD to digital circuits. You can decouple the processing from the storage (the disc) by using a RAM buffer for intermediate storage. |
Transports are not perfect i.e once in a while they make errors but these errors are detected and corrected by a digital circuit. If the system makes a huge amount of errors, such as when your car CD player skips when you drive thru a bump on the road, then you will hear this. A skipping CD player is an example when too many errors are made which "overloads" the error correcting capability of the circuits.
Note that we a talking about a digital means of data delivery. This is not an analog system like a turntable where subtle issues i.e. spin rate of the turntable can be coupled into the music. The digital system with transport is tranferring 1's and 0's into RAM. It does this with the utmost reliability. Dont forget you are trusting such a system of data transfer when you use your computer on a daily basis. |
Germanboxers, I would like to emphasize that you are right; the transport is very important. It is responsible for getting the data correct. However, getting the data correct is very easy and very inexpensive and very trivial. All PCs today rely heavily on CD/DVD transports doing their job well. In a PC, when a transport fails, you throw it in the trash and get a new one. |
Germanboxers,
Yes, the 1's and 0's are represented with voltages. But unlike an analog system where any slight deviation is considered distortion, the digital system is orders of magnitude more impervious to signal variation. Here is an example.
Consider a typical system where 0V represent a "0" and 3V represent a "1". For a "1" to be mistaken as a "0" the 3V will have to drop below 1.5V. In the analog circuit case any variation is bad but for the digital case the signal has to lose half it's value before a mistake is made.
Another way to think about this is that in an analog amplifier, the designers have to make sure that distortion is below say 0.1%. But for a digital system, you can tolerate up to 50% signal change (i.e. 3V dropping to 1.5V) before one error is made. Furthermore if an error is made, the use of error correction fixes this issue.
I can say for certain that the data read from a transport after error correction will be ZERO (unless you're thumping the player with a hammer). If this is not the case you have a defective unit and you should get it replaced. Furthermore, if your defective unit is producing bit errors, you will definately hear it. It will not sound like "the soundstage of the music has narrowed". It will sound someone turned on the juice blender for a brief period.
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Germanboxers,
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So, you are saying that mis-reading a "0" for a "1" or vice-versa with some random frequency will cause the sound to become like a blender? It won't just misrepresent the amplitude value of the complex wave at those particular sampling points? Assuming a .1% error rate, that's still 40 some errors in amplitude resolution/sec.
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It is due to the way PCM is encoded. Once again do not think of this as an analog signal. For CDs you have data which is 16 bits long. If any of the LSBs (least Significant Bits) were transfered in error, then you would probably not notice this. But as you mentioned since this is random, any of the 16 bits could be transfered in error. If any of the bits which did not reside among the lesser significant bits were corrupted the amplitude error would be huge. Yes, it would actually sound worse than a blender. Just think of what happens if one iota of a note went from very soft to very loud almost instantaneously.
Fortunately, this never happens for a properly designed player. Because there should be ZERO errors after error correction. Like I said, if your transport is failing, you will know it. It is not subtle. |
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Any current $150 universal player uses powerful DSP and memory buffering which according to your and Lktanx theory is sufficient to do the job providing error and jitter free data output. Why don't you get one of these and hook it up to an external DAC together with your x1 reading and non-memory buffering VRDS Wadia and see which one will sound better? I can tell you right now; your Wadia will be a LOT better. Also, when you were talking about your friends computer based audio with external DAC did you try your Wadia as a digital transport through the same external DAC? If you have not, please do that and let us know if the computer based error free transport can provide the same bass extension and the same top octaves clarity, air, openness and resolution as your Wadia will.
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Alex,
I am only discussing transports and their associated error correction circuitry. Let's not compare different issues. Of course a Wadia will sound different than a PC playing a CD. This difference is not and should not be due to the transport and error correction. This is because both the Wadia and the PC possess transports/error correction circuitry which produce ZERO errors.
The Wadia sounds different because it has a different clock reference with different jitter characteristics. The Wadia also has different digital filters and DAC. So obviously they should sound different. Nevertheless, I will not state which sounds better.
I am not claiming that all CD players sound alike. I am claiming that a properly designed CD player's sound should be completely uncorrelated with the transport. The sound will be a function of the following (not in any order of importance):
1. Digital filters
2. DAC
3. Clock reference
4. Clean analog power supply
5. Output driver stage of DAC
Note, the transport/error correction circuit is one thing engineers can do perfectly, inexpensively, repeatably, and in large quantities.
I am purely speculating on the actual numbers but here is an example:
High end transport = 1 error per minute
Cheapo transport = 100 errors per minute
Obviously the high end trasnport is better here. Now with error correction:
High end trasnport with EC = 0 errors per minute
Cheapo transport with EC = 0 errors per minute
I hope this helps you decide where to invest your hard earned $. |
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Again, I don't know about audio CD players, but in the world of computer data if there was any substantive liklihood of that sort of undetected error from a CD read occurring, then how often would software installed from a CD fail to operate becuase what was on the hard drive did not match what was on the CD? Note that I'm not talking about corrected errors. In all the years I've spent installing software from CDs (assuming the CD was not damaged in some way) I have never had that happen. Not once. Ever.
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I would like to further emphasize Tonyptony's statement above. With music CD players, the drive mechanism is running at 1X. When you install software, the latest PC CDROM drives are running at 48X or even higher. If the 48X drives are not producing errors, just imagine how trivial a 1X drive mechanism is with today's technology. |
We may have gotten a bit side tracked from my original response. Here is a very simple example of why a transport makes no difference. We build the following hypothetical system. This system consist of 3 boxes interconnected. They are:
A. Transport only
B. RAM only
C. Digital filters/DAC/Output stage
These 3 boxes make up a complete CD player. The following lists a step by step process to listen to music.
1. Download entire song from Transport into RAM, error free of course.
2. Turn OFF Transport and disconnect it from RAM.
3. Discard Transport into an incinerator and burn it.
4. Play music from RAM thru box C which has the digital filters and DAC.
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