I would like to argue that one of the reasons that some transports sound significantly better than others is because much of the information on a given CD is actually analogue (analog) information. An excellent transport does not just read digital information: 1s and 0s (offs and ons); it must be sensitive enough to pick up the other information that has been stored as a physical property of the CD medium. This 'physical' information, like the tiny bumps in the groove of a vinyl record, is analogue information.
Before I say more I'd like to hear what others think.
Onhwy: The digital recorder that i was using was a stand alone TDK CD-R Audio burner. I purchased this unit based on the reputation that the TDK computer based burners had at the time i.e. as being the best and most reliable at the time for pennies on the dollar. Most of this had to do with their software, which included specific "tricks" to minimize errors, data correction and "glitching" due to a lack of buffering.
From what i can remember, i think that the ADC's and DAC's in this unit were made by AKM, which is the brand that Shadorne mentioned above. I would have to pull this unit apart to make sure, which i will do if you guys really want me to.
Obviously, this is not a "high tech" or "ultra resolving" unit. Then again, the original analogue tapes were made on a DC powered portable monophonic Marantz unit. Even so, the recordings made on the Marantz unit sound more realistic in terms of tonal balance than the direct feed "dubs" made via the CD burner. As i previously mentioned though, the digital dubs should have simply recorded what was being presented to it, NOT shifted the tonal balance in quite noticeable fashion.
As far as recording using a computer or sound card based device, i wouldn't bother. That's why i bought the stand alone Audio based burner. Sean >
What many want to argue is that the difference between a good sounding digital front end and a bad sounding one essentially comes down to jitter (jitter in the time domain). In other words, its easy to get all the information off a disc, CD players, DVD player, CD drives in computers, all do an excellent job of extracting the information from CDs. The hard thing is to deliver all those bits of information to the DAC at precisely the right time.
I actually find it hard to argue with this. After all, if the crappy CD drive in my computer missed picking up the information off a CD, the program (or whatever was on the disc) wouldn't run! I also understand how hard it is to deliver all those bits of information to the DAC at precisely the right time in order to make music.
What conclusion does this lead to? It leads to the conclusion drawn on an excellent site on jitter (jitter.de) that is written by the maker of excellent digital equipment. Here it is argued that all you need is a transport (any cheap transport will do) to send digital information, timing errors and all, to an EXCELLENT clock that is positioned right in front of the DAC. The excellent clock will re-clock all the perfect data that has been sent thus removing all the jitter. The DAC will then have all the information, nearly perfectly timed aligned, to then convert to analogue.
This sounds really good in theory and it will be my hypothesis going into a controlled experiment to see if it is actually the case. If the experiment shows that different transports sound significantly different when feeding the same clock and DAC, we will have to scrap this hypothesis. I know that it will be hard for some of you to do but the scientific method demands it.
Some suspect that we will be looking for a new hypothesis after my ML 31.5 CD transport ends up sounding better than my DVD player. If this is the case, then, in the name of science and the honest and noble pursuit of knowledge, we can all start working on a new hypothesis. And those who continue to argue that transports DON'T make a difference because, in theory, they SHOULDN'T make a difference, will be politely ignored.
Currently, I do not find differences in DACs to be subtle. I find many DACs to be un-listenable and others to be quite good. Some DACs sound 'confused' while other sound 'right.' When it comes to transports, some sound threadbare and anemic while others are full-bodied and create an excellent sense of space. I have also experienced significant differences between digital cables (see my review of the Stealth Varidig Sextet, for example).
When I first started building a high-end system, however, the difference between various digital front ends was indeed subtle.
Take an analogue source, record it onto a CD and then compare the original analogue source to the digital "cloned" recording using the same playback equipment. If you can't hear the difference between the original and the "digital clone", you better check into the office of an audiologist for a very thorough exam. You are either going deaf and / or are thoroughly lacking in listening skills.
By your definition I am deaf and thoroughly lacking in listening skills. I admit that I often can't tell whether my AKM ADC & DAC converters are in the signal path or not. What equipment are you using that you hear such a huge difference....a PC sound card?
Sean, please name your digital recorder. The implications of your comments is that A/D conversions cannot capture any analog signal, whether a line feed from a microphone or the output of a tape deck. Even professionals who prefer analog recordings have admitted that high resolution digital is more faithful to the original sound.
I'm comparing apples to apples here. In the tests that i performed, i used live analogue recordings that i had made. These recordings had no form of compression, equalization, etc.. performed on them. I then converted them over to CD via an audio based digital recorder that i have. The end results were that the digital "clones" weren't clones of the original analogue signal at all, but bad recordings that barely resembled the originals in terms of tonal balance.
Using this same digital recorder, i've made very good "dubs" of other digital recordings. As such, the losses incurred going from analogue to digital are FAR more severe than when working strictly within the digital domain. This is probably why so many of the early "AAD" discs sounded SOOO bad. That is, they were recorded and mastered in analogue form, but sold as recordings in digital form.
Given that i've had similar results using other digital based recording devices that i have access to, i know these results to be both consistent and repeatable. This is why i said what i did above i.e. others can find out for themselves by performing just such a test. Sean >
Sean...Did it ever occur to you that the "TONS of equalization" that you say is applied to digital recordings may actually be the removal of equalization that was applied to make vinyl sound good? There are several digital recording labels that claim to use no electronic equalization or other processing at all.
Here's a simple task that most everyone with a stand alone CD burner or computer based burner can do. That is, if they have the desire and means to do so.
Take an analogue source, record it onto a CD and then compare the original analogue source to the digital "cloned" recording using the same playback equipment. If you can't hear the difference between the original and the "digital clone", you better check into the office of an audiologist for a very thorough exam. You are either going deaf and / or are thoroughly lacking in listening skills.
Until one has done something like this, making comments about this subject is useless and a waste of everyone's time. Anybody that has done something like this will know why older analogue recordings pretty much HAVE TO BE remastered when released on CD. That is, they have to apply TONS of equilization in order to get something that even remotely resembles the "natural" tonal balance that was lost when converting to digital. Sean >
PS... making digital to digital copies typically results in excellent copies. When going from analogue to digital, even using the shortest and purest path possible, it all goes to hell.
I have found differences in DAC's but these are usually very subtle, most often a slight difference in the treble and often not enough to make me worry that much. The only relatively much larger differences I have come across are all associated with analog gear (particularly mechanical systems that vibrate; such as speakers, listening room and turntable cartridges, and to a lesser extent tube amps, which add a bit of their own nice flavor to the sound).
My comments are relative - no doubt there are differences between CD players and improvements can be had for big $$$ but I would have difficulting in calling these differences "huge".....is there a particular CD player that you have in mind that sounds hugely different from others?
As far as digital sounding so bad...perhaps this is a matter of taste. IMHO, I find digital sounds more accurate and detailed....some might call this harsh and brutal but my perception is that it is more realistic....too each his own. When I used analog I used to buy Japanese pressings because they sounded better but now that I use CD it makes no difference where the CD was pressed (althouogh the quality of recording/mixing and mastering remains very important)
Some computer geek ought to record the digital data stream (after error correction)as generated by two or more transports. Then write a program to time slip one file until it syncs up with the other, and then do a bit by bit compare of the files. I bet they will match perfectly.
There may be other transport characteristics which affect sound. Jitter is often quoted. What if one transport ran slightly faster or slower than the other. Quite small pitch changes affect music.
In some metaphysical sense there is no real distinction between analog and digital information, but practically speaking, particularly if we exclude the printed info on the CD disc/packing, 100% of the data (music) contained on a CD is digitally encoded. I honestly don't see how someone can get so confused on this issue.
Bob Reynolds: I adamantly believe that transports have a sound of their own. Whether or not they are discernable has to do with how different they sound and / or the resolution of the rest of the system and / or one's hearing acuity.
My Brother and i have conducted testing using several different transports. Some of the differences were not only quite audible, but quite staggering as far as how different the same discs sounded with the transports being the only variable. We were even using impedance matched cabling, so RF based digital reflections that cause jitter were taken out of the picture.
There was something else that we both learned while doing this. The primary sonic characteristic that we heard from each of the players ( when being used as a player ) were also prominent when using them strictly as a transport. When a machine sounded warm and round as a player, it also sounded warm and round as a transport, etc...
As such, the only logical thing to surmise from all of this was that the transport mechanism, laser assembly, power supply circuitry, digital correction circuitry, etc... contributes a LOT more of what we hear than what most people think. Sean >
I am afraid the IAR stuff does not agree at all with mathematics and science.
There are indeed many deficiencies in digital, it is far from perfect;
- proper filtering must be applied in the studio prior to digitizing a signal in order to avoid aliasing (stuff that is not filtered folds in around the Nyquist frequency).
- high out of band noise is common on most DAC's and must be heavily filtered (this is not ideal but generally not a problem for well designed gear with oversampling etc.)
- clock jitter can affect sound particularly if the jitter is not random. (again proper design has corrected this in most, if not all, commonly available gear)
Contrary to IAR, the details in the waveform are NOT lost in digital. In fact they are preserved much much more precisely than analog.....way better S/(THD+N) and way better channel separation.
If you don't believe it then STOP using your COMPUTER now .....becuase it is ALL based on similar technology....your disc drive uses Solomon Reed type algorthims too!!!! Almost all digital technology uses these concepts to make digital copies extremely accurate.....1000's of identical copies can be made with never a single error.
In fact digital is so good that the whole entertainment industry is scared of how downloading and piracy of digital data can undermine the control of legal distribution of high quality music and video.
In fact digital or binary type coding is so good that it forms the basis for all lifeforms that we know of on this planet! Yep, your DNA is basically a digital coded string in the form of a double helix - http://en.wikipedia.org/wiki/Double_helix
The genetic code consists of three-letter 'words' (termed a codon) formed from a sequence of three nucleotides (e.g. ACT, CAG, TTT). These codons can then be translated with messenger RNA and then transfer RNA, with a codon corresponding to a particular amino acid. There are 64 possible codons (4 bases in 3 places or 4*4*4 possible "digital" states) that encode 20 amino acids. Most amino acids, therefore, have more than one possible codon. There are also three 'stop' or 'nonsense' codons signifying the end of the coding region, namely the UAA, UGA and UAG codons.
DNA does not appear to use Solomon Reed encoding but it is very robust digital code, such that every cell in your body contains the same digital information, which is why cloning is possible....something way scarier than music piracy, IMHO.
From the wiki link: "In the same sense that one can correct a curve by interpolating past a gap, a Reed-Solomon code can bridge a series of errors in a block of data to recover the coefficients of the polynomial that drew the original curve."
Put your CD player on top of your speaker and listen to how wonderful error correction sounds. Using a mathematical algorithm to fill in gaps and help plot a wave by taking 'best guesses' sounds exactly how you'd expect it sound.
Principles of Digital Audio, fifth edition by Ken C. Pohlmann. McGraw-Hill.
I got it from the library. (It is $60 at Amazon.) It covers not only CD, but DVD, DVD-A, SACD, MP3 and a lot more. There is a good amount on transports as well.
It didn't make me an audio engineer but I did learn enough to calibrate my BS meter.
The CD data retrieval process is actually very different from phono playback.
Under normal conditions the CD transport will retrieve an exact copy of the digital data used to create it (think CDROMs - computers won't tolerate a "close approximation" of the original data). The CD contains a large amount of redundant data in the form of Error Correcting Codes (ECC).
Data is not read from the CD in a linear fashion like a record groove. The data is stored along and read in in blocks. Each block is protected by ECC code and contains subcode (including timecode - this displys in the transport time window).
Also the laser doesn't translate individual pits into bits. Instead pit patterns, called symbols, translate into bit patterns. These pit patterns are designed to be easy for the photodector to read. Finally the blocks of data are not recorded linearly but are reordered and spacially seperated from each other on the disk. This reduces the likelyhood of a scratch rendering the disk unusable.
The transport reassembles the data blocks in the correct order and uses the ECC codes with a mathematical algorithm to detect and correct all single symbol read errors and detect almost all multiple symbol read errors.
For multiple symbol errors the player may resort to error concealment, where it generates some best fit data to fill the gap. Worst case it mutes the output momentarily (a skip). Multi-symbol read errors are extremely rare on disks in reasonable condition.
The biggest issue with transports seems to be clocking accuracy of the output datastream. With proper engineering this can be almost independent of the physical reading of the disk. The transport can read ahead of the actual listening point, buffer the data in memory, and clock it out at a highly accurate rate.
Good eye pattern helps the accuracy of symbol reading and reduces the need for error correction.
Fascinating. Is there a reference in the audio, or preferably, engineering press you could point out? I always thought the thing that separated good from great transports was the degree to which they reduced and/or corrected misreads, which can be due to sloppy CD manufacturing processes, dirt, etc...
One of things that I was refering to is the "analog eye pattern". Contrary to popular opinion, tranports take analog information from a CD and 'build' a digital signal. Only then is the digital signal sent to the DAC for conversion back to analog. The sound coming from our speakers is only going be as good as: 1. the transport's ability to pick up the raw analog input signal as a reflection of the laser bouncing off the CD (the 'eye pattern'). 2. the transport's ability to use this analog information to create and generate a digital bit stream that is a close approximation of the digital bit stream that existed in the recording studio.
Because the disc is, in a sense, an analog representation of a digital data stream, the raw data is imperfect. But we don't listen to raw data. Corrupted data is to be expected, and the signal information is encoded with an error correction algorithm that yields "clean" data.
The pits only serve to provide digital iformation which requires translation. The reason for integral or external DACs is to translate the digital (not analog) to analog otherwise you couldn't get anything from the pits. If you mean analog is defined as something physical with a surface that provides information in a digital format. Then OK I guess? but that is not what analog means to virtually everyone else.
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