Error checking and correction is very loose in CDPs since it has to read CD in real time (dust, scratches). There are programs like MAX for Mac that read music CD as data going multiple time to the same sector until finds right checksum. My CDP plays and Itunes rips CDs that MAX refuses to read or reads extremely long time.
Digital data from CDP is jittery (contains jitter - noise in time domain). Jitter creates sidebands at very low level (in order of <-60dB) but audible since not harmonically related to root frequency. With music (many frequencies) it means noise. This noise is difficult to detect because it is present only when signal is present thus manifest itself as a lack of clarity. Jitter can be suppressed by asynchronous upsampling DACs (like Benchmark DAC1) or reclocking devices. Jitter depends on quality of CDP transport and power supply. Typical digital transition of CDP is in order of 25ns making it susceptible to noise (slow crossing of threshold). High quality transports can transition many times faster reducing noise coupling but creating a lot of problems with reflections on cable characteristic impedance boundaries (therefore require better digital cable).
Jitter in D/A playback can be suppressed but recorded jitter in A/D process stays forever. For some early A/D conversions the only option is to convert it again if analog tapes still exist. |
It's not just 0s and 1s..... page 54 |
To the OP: Take it from another EE; your friend is correct. Everything that matters as to signal quality occurrs before and after the digitization. You cannot do anything about what happens before the signal is digitized so if you want to improve quality concentrate on what happens afterwards. Moving the digital signal around is not a place to spend any effort. |
Stanwal, the problem that you are describing is properly ascribed to the DAC or the output stage, just like Shadorne said above (twice).
Trust me, if the 0's and 1's were getting messed up, it would not be subtle, but horrible--like the sound of a skipping CD. Your computer would tell you that it can't read that CD, etc.
Horrible, catastrophic errors--those probably come from a bad reading of the 0s and 1s. Subtler, "audiophillic" errors--those probably come from an inferior DAC or output stage. |
The problem with the just 1s and 0s is that it simply doesn't hold up in practice. To repeat a story I have alluded to before, years ago a large Japanese CD pressing firm send [I think] HiF News some different pressings of the same CD, some with standard material and some with a mix of materials that would cost slightly more and which they were attempting unsuccessfully to get the record companies to adopt. There was such a huge difference in sound between them that they had to download them into a computer to see if the data was the same. It was exactly the same, if digital is so foolproof what made the difference? The laser system is a mechanical one and constitutes a change from analog to digital, they are not ones and zeros but REPRESENT ones and zeros in the same way the groves in an LP represents sound waves. Many mechanical factors can interfere with the ability to correctly read the pits and translate them into digital signal. |
Ever hear a CD "skip"? That's when the quality matters.
The distortion from a bad reading of 0's and 1's will most certainly not be euphonic.
So if your tone-deaf buddy/brother/significant other/etc. that thinks that you're crazy to spend all that time and $$ on your stereo listens to your system and immediately tells you "dude, your CD is broken", then you've got a problem with the quality of your digital signal. If such a person does not immediately point the finger at your CD player, then you don't have a problem with your digital signal.
Don't worry, you will find other problem with your stereo--I know I have. :) |
I'm glad to see some objective insight on this subject. Keep in mind that I'm making a clear distinction between the two cases of having analog vs. digital being output from the CD player.
In my mind, a clean analog system would be the following:
(1) turntable - pre-amp - amp - speakers
In the digital world it would look like one of the following:
(1) CD player (DAC) - pre-amp - amp - speakers
(2) CD player - seperate DAC - pre-amp - amp - speakers
(3) CD player - integrated DAC/amp / receiver
I suspect that having an analog signal go through my home theater receiver would probably cause more degradation of the signal quality to nullify any advantage of an auidophile grade CD player.
I do not think that timing would be an issue for CDs as most can read a disk much faster than is required. This is was is known as a buffer and we all know what happens on youtube when the buffer isn't adequate.
My thought is that someone that will be using a home theater receiver (possibly other options depending on budget) would do better to put their money towards a better receiver and speakers than to invest in an expensive CD player and increase the number of things in the analog signal stream.
The issues assocated with degradation begin wherever the D/A happens. |
keep in mind that while digital info is just 0's and 1's there also has to be a timing element that insures that the bits are in the correct place. Easy to get them in order but if your disk is spinning too fast then your read is too fast and such. Mind I'm not advocating anything as I am suspicious of so many things here but I could see timing perhaps being affected by cheap stuff. One problem with isolation is that there is a delay between setups and the listener often knows which is which. Any blind tests out there with multiple listeners and under statistical or sampling control? |
Just 0s and 1s? Then there is this...... |
If Shadorne's argument is correct then why should the quality of the DAC or CD player matter? I think I covered this: In fact the biggest source of quality differences with digital audio is the conversion to analog - this is where differences are audible - in the quality of the D to A converter. Clock & converter accuracy as well as the quality of the analog circuitry in the output stage can still make a difference. However, digital eliminates the problems of media storage degradation and analog read errors from media. (dust, feedback, surface noise, pressing imperfections, pre-echo, poor chanel separation, lack of dynamic range of analog storage methods etc.) |
CD's are not 0s and 1s. They are pits burnt into the metal layer and are measured for lenght by the lazer and then converted into a digital format. These pits (or the transition) represent bits: a 1 or a 0. All digital information must be stored in analog form including what is on your computer hard drive. However, the digital approach allows the use of a threshold level or clear demarcation between a 1 and a 0 that does not exist in analog approaches. Example of a digital scheme (not from a CD) Signal level between -.5 and +0.5 Volts = 0. Signal level between +0.51 to 1.5 volts = 1. This means you can have a lot of analog error or noise in the media and still get a perfect translation of the data as exactly what it should be - a 1 or 0. If you add parity bits or polynomial redundancy check bits to the data you can also improve the robustness further (allows detection of data errors or even allowing for recovery of completely missing data) Using the same example, compare this to an entirely analog approach where the difference between 0.O and 0.4 volts may be significant. |
If Shadorne's argument is correct then why should the quality of the DAC or CD player matter? Even cheap one seem to measure very well. "Signal quality much less of a factor than in analog"? No wonder my LPs sound so much better. Why do transports make such a difference? A friend of mine didn't believe they would until he heard different ones on his system. Why do the best CD playback systems cost so much unless they are susceptible to degradations just as analog is? |
CD's are not 0s and 1s. They are pits burnt into the metal layer and are measured for lenght by the lazer and then converted into a digital format. Then they are run through a Digital to Analog converter. |
This is something laypeople never seem to grasp. The entire advantage of digital is just that = "signal quality matters much less than analog".
This is a FACT.
The idea of representing information as 1's and 0's means that information can be stored and transmitted with no loss - something that is IMPOSSIBLE to achieve with analog.
So I would say YES - signal quality is much less of a factor in digital than in analog.
In fact the biggest source of quality differences with digital audio is the conversion to analog - this is where differences are audible - in the quality of the D to A converter.
You can copy a CD with a cheap drive 1000 times and it will be the same (copy of a copy) however it will sound better with a dedicated high quality DAC or a good quality CD player. |
From How Stuff Works:
"In analog technology, a wave is recorded or used in its original form. So, for example, in an analog tape recorder, a signal is taken straight from the microphone and laid onto tape. The wave from the microphone is an analog wave, and therefore the wave on the tape is analog as well. That wave on the tape can be read, amplified and sent to a speaker to produce the sound.
In digital technology, the analog wave is sampled at some interval, and then turned into numbers that are stored in the digital device. On a CD, the sampling rate is 44,000 samples per second. So on a CD, there are 44,000 numbers stored per second of music. To hear the music, the numbers are turned into a voltage wave that approximates the original wave."
What this means is that until the numbers of the digital signal are converted back to a analog voltage wave via a D/A converter the only thing that matters is that the signal be transferred.
Maybe this is my my CD player recommends using a digital connection to my receiver rather than analog. At my equipment level he preservation of the analog signal isn't able to match bypassing the component all together and "shortening" the path of the analog signal. |
That's exactly the question. I would suspect that the vast majority of audiophiles use analogue connections to avoid ever having to make the transition into a digital format.
If a CD player is doing nothing more than reading the digital data (i.e. ones and zeros) on the disk and sending the information to another component for the D/A converstion what could effect the signal?
Do you insist on having a $1,000 CD drive in your computer to ensure that you have an accurate copied disk? How about burning a disk on an external drive using a USB cable, is there any risk of not getting a perfect duplication of the original without getting an error? |
Of course not, these expensive CD players are just a rip off. Since the cheapest ones at Walmart are already perfect what use is there in paying more then $59.95 for one? |
