大家常常在討論這個D vs A 的問題....
我轉貼一下這篇文章....
Back to Analog-Why Retro Is Better and Cheaper
This article has been revised and updated from an editorial counterpoint which appeared in Pro Sound News, January 1997. Here's a refreshing alternative perspective to what's going on in the studio scene for everyone from musicians to owners of Project Studios to large studios.
Analog Audio vs. Digital--The Good, The Bad, The Ugly
Doing analog audio in the sixties and seventies was hell. Most of us would like to throw our bias oscillators in the garbage. Analog requires constant vigilance to sound good. In addition, you can't copy an analog tape. The second generation just falls apart; it's a pale replica of the first. If analog's so bad, what's the problem with digital recordings? We can give them the warmth of analog if we use vintage tube mikes and analog processors, right? There must be something to that argument, or the whole industry wouldn't be doing the retro-tube trip in 1996. But I wonder if we're all doing it for the wrong reasons. Please remember that there's good tube equipment out there, and a lot of bad. There's also good digital equipment and an awful lot of bad. Much tube equipment is overly warm, fuzzy, noisy, unclear and undefined. Only the best-designed tube equipment has quiet, clear sound, tight (defined bass), is transparent and dimensional, yet still warm without being artificial or muddy. Similarly, most of the cheap digital audio equipment is edgy or hard-sounding, dimensionless, and unclear. Only the very best digital audio equipment (and it's getting better every day) can lay claim to good soundstage width and depth, purity of tone without an artificial edge, and transparency.
Bad Digital versus Good Digital
Many people have argued that digital audio recording is more accurate than analog, saying the accuracy of digital is why we're noticing hardness and edginess in our recordings, and have regressed to tube and vintage microphones. That's only a half-truth. Let's distinguish between bad digital and good digital equipment design. Bad digital (which includes the 16-bit A/D/A's in most integrated recorders) sounds bad because it is bad. Bad digital equipment has distortions that innately increase edginess and hardness. Edgy sound can be caused by many factors: sharp filters, poor conversion technology, low resolution (short wordlength), poor analog stages, jitter, improper dither, clock leakage in analog stages due to bad circuit board design and many others. Placing sensitive A/D and D/A converters inside the same chassis with motors and spinning heads is also a dangerous practice. It takes a superior power supply and shielding design to make an integrated digital tape recorder that sounds good; compare the sound of an inexpensive modular digital multitrack (MDM) with the Nagra Digital recorder.
I receive many edgy-sounding, dimensionless DATs that went through the MDMs and the digital consoles which now can be found at project studios. Through loving care and a number of proprietary processes in the mastering stage, I can bring these DATs up to a much better quality level. It is possible to give the sound greater apparent transparency, more spaciousness, increased purity of tone, improved dynamics and transient response (where these changes are esthetically appropriate). A mastering engineer who has made and heard the best recordings can do a lot for these DAT tapes. But let's not forget the sound that can come from analog tapes mixed through analog consoles, and from widetrack analog masters. After reading this article, I think you'll reconsider the analog alternative.
Band-Aids Instead of Cures
Bad digital benefits from the use of tube mikes and preamps because their warmth and noise help cover up the hardness of the rest of the signal chain. Use of warm-sounding mikes and preamps can become a fuzzy blanket that hides the potential resolution of the system, but it is not a cure, it is a bandaid. Even good digital benefits from proper choice of microphones and preamps (including well-designed tube equipment). Digital recording is considered to be "accurate", but each of its specs must be considered carefully. Consider its linear frequency response. With bad digital technology, linearity of frequency response can turn from virtue into a defect. We can no longer tolerate the distortion and brightness of some solid-state equipment (including poor A/D converters, microphones and audio consoles) because digital recording doesn't compress (mellow out) high frequencies as does low speed (15 IPS) analog tape. To summarize: digital recording can sound edgy for two reasons. One is linear frequency response, which reveals non-linearities in the rest of the chain. The other is built-in distortions in the A/D/A conversion process.
The Virtues of Analog Recording
Listening to a first generation 30 IPS 1/2" tape is like watching a fresh print of Star Trek at the Astor Plaza in New York. I believe that a finely-tuned 30 IPS 1/2" tape recorder is more accurate, better resolved, has better space, depth, purity of tone and transparency than affordable digital systems available today. Empirical observations have shown that you need at least a 20-bit A/D to capture the low-level resolution of 1/2" 30 IPS. It can also be argued that 1/2" tape has a greater bandwidth than 44.1 KHz or 48 KHz digital audio, requiring even higher sample rates to properly convert to digital. Listening tests corroborate this. 30 IPS analog tape has useable frequency response to beyond 30 KHz and a gentle (gradual) filter rolls off the frequency response. This translates to more open, transparent sound than (almost) any 44.1 kHz/16 bit digital recording I've heard. 1/2" 30 IPS analog tape has lots of information, like high resolution 35 mm film.16-bit 44.1 KHz digital is like low-resolution video. As higher resolution (96 Khz/24 bit) digital formats become the new standard, maybe then we'll be able to say that digital recording is better than analog. But don't be fooled by the numbers; poorly-constructed converters, even at 96 kHz may produce distortion products that are more objectionable to the ear than analog tape. Analog tape has its own problems, but when operated within its linear range, unlike digital recording, it has never been accused of making sound "colder".
The Real Cure
A 16-bit modular digital multitrack needs a lot of expensive help to sound good. Naked, a typical MDM (with its internal converters) sounds hard, pinched, edgy, and undetailed. Mix it down to 16-bit DAT and you're doubling the damage. It is possible to modify the electronics in the MDMs to improve them. The first way to get reasonable-sounding digital is to add external A/Ds and D/As which may cost several times the price of the basic machine. That'll restore a lot of the missing purity of tone, space, and detail, and reduce the edginess. The entire modular 8 track recorder costs less than a 2-channel A/D converter from the best audio firms! This points out the large economic disparity between "bad" and "good" digital. It's obvious that to have good digital sound, your project studio can quickly become a million-dollar venture.
At first glance it may seem that using a digital console to mix down from MDM can be an advantage, because you are not using the poor D/A converters in the MDM, but now you will have to deal with the long wordlengths produced by the calculations in the digital console. Using a 24-bit MDM and 24-bit 2-track help a lot, as long as you minimize multiple passes through the DSP circuitry in the console. Numeric precision problems in digital consoles produce problems analogous to noise in analog consoles. However, there is a difference between the type of noise produced in analog consoles and the distortion produced by numeric problems in digital consoles. Noise in analog consoles gradually and gently obscures ambience and low-level material and usually does not add distortion at low levels. Numeric problems in digital consoles can cause several problems. Rounding errors in digital filters act much like analog noise, but at other critical points in the digital mixing process, wholesale wordlength truncations can cause considerable damage, destroying the body and purity of an entire mix, creating edgy sound, which audiophiles often call "digititis". Depending on the quality and internal precision of the digital console and digital processors you choose, and the number of passes through that circuitry, it might have been better to mix down to analog tape through a high-quality analog console.
If you do not use an analog mixing console in conjunction with "old fashioned" analog equalizers and processors--- you'll have to take extra pains to make your digital system sound close. If you can't afford high-quality external A/Ds (and 20-24 bit storage), there are other approaches. The band-aid, of course, is to buy some expensive tube mikes and cover the evils of the cheap A/D/A's and processors. You'll get a warm, fuzzy sound, but that's preferable to a hard and edgy one. In other words, good digital is expensive and probably the best you can get from bad digital is "warm and fuzzy"!
I prefer the real cure. It's cheaper, and better-sounding. Go back to analog tape! Invest in a great analog recorder. Your first step is to get a good two-track 1/2" machine. After that, consider getting rid of your 16-bit MDMs and replace them with a wide-track analog multitrack. To get good analog sound that's better than most affordable-digital, practice your alignment techniques, don't bounce tracks, use wider track widths and higher speeds than you did before. It's orders of magnitude cheaper than 24 tracks of 96 Khz/24-bit digital audio.
Making the Right Tradeoff Decisions
If you must choose some digital storage and processing, evaluate the tradeoffs carefully. Depending on the type of music, an all 96/24 system might sound better than the 30 IPS, but not by much. Both media are clear, detailed, warm, spacious, and transparent. We have to reevaluate the tradeoffs each year. For example, in the year 2000, the cost of 2-track, 96/24 digital recorders has plummeted, with the introduction of the Alesis Masterlink at around $1500. This machine may replace 2-track analog, but will only perform at its best with external converters costing twice as much as the machine! Study the compromises and look at each situation as a tradeoff: If you have too much "digital", and not enough "analog", your results will not be "fat" or "warm" enough. And perhaps vice-versa! So, don't pick too much from either column! If your "digital" processing and storage is at 48 kHz instead of 96K, consider the analog console and outboard or you will have too much "digititus". Note in the columns below I suggest the best of each category. If you compromise by using the 2-track digital recorder from Column "D", with internal converters, which can sound a bit harsh or unresolved, consider even more components from Column "A" to offset the harshness. Another possible compromise is to use a low-end digital console. The mixing resolution in these consoles is usually "adequate", but often the equalization and compression less than pristine. In that case, if you must mix digitally, then think about using high quality outboard analog processing, to avoid cumulative digital "grunge".
ANALOG OPTIONS DIGITAL OPTIONS
2" 24-track 30 IPS Analog 24 track 96/24 Workstation or Recorder with external converters
2-track 1/2" 30 IPS Analog 2-track 96/24 Recorder with external converters
High end Analog console High end 96/24 Workstation or Digital Console
Analog Outboard Processing Digital "Plugins"
With today's choices, you can offer musicians a real value that sounds great. You can easily assemble an affordable multitrack system that sounds better than the old 44.1/16 MDMs. When economics are a consideration, consider putting together a hybrid system that contains the best of analog and digital. It can sound great! I'm looking forward to seeing your fabulous tape at our mastering house!
This is Artical is from digido.com
轉貼!! Digital VS Analog from Digido.com
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