At 24-bit, Dobro, you don't even have to worry about it - the scale of resolution is so much greater that you basically can put the meters ANYWHERE you want and have a great sound... but to more specifically answer your question, when you record more quietly, you are not using the full 24-bits to represent your signal - but the resolution is high enough that it needn't concern you. The specific meter ranges, though, I'll have to get back to you on (research!)....
In the meantime - here are a couple of (long!) articles from Bob Katz, related to this:
Aren't 20 bits good enough?
From: "Arksun" <arksun@arksun.co.uk>
Hiya Bob, Hows tings.
I was wondering whether you could settle a long running argument between myself and a producer friend of mine. My friend Andrew
Longhurst believes that for A/D conversion there is absolutely no need to go greater than a 20-bit convertor, as the noise level is significantly
high enough in an analog cable connection that a 24-bit convertor would offer no sound improvement what-so-ever.
Dear Laurence:
Things are great, very exciting, and very controversial. The future of the mastering industry keeps on shifting.
Anyway, to prove your point, you'd have to have an A/D converter with true 24 bit dynamic range, whose noise level is that low.
Most so-called "24 bit" A/Ds have only approximately 20 bit dynamic range in the first place! But arguably, may have resolution
below that number. The only A/D perporting to have true 24-bit dynamic range that I know of is the dB Technologies, which I have
not auditioned or tested. And then, you must conduct a controlled experiment. It's possible that your friend is right, but I leave no
stone unturned, and only a controlled listening experiment would settle the issue. In theory, your friend may be right, but it has to
be settled on the basis of masking theory, and masking theory demonstrates that you can hear signal quite far below the noise in
certain frequency ranges. Maybe 21 bits, maybe 22...it's hard to say, but I believe it is *marginally* greater than 20 in the case
cited above. But in the same vein, in theory, it seemed that a 16-bit converter should be adequate to record an analog 1/2" 2-track
tape as the noise level of the analog 1/2" is far greater than 16-bits, but in practice, it takes a high quality converter of at least 20
bits to do justice to an analog tape, so as far as I'm concerned, all bets are off until they have been proved by listening tests. That
goes for all assertions of theory versus practice, by the way!
I on the other hand am looking at it from the 'real-wave' representation point of view, and am arguing that it's precisely because of this
further wave form complication induced by noise that the highest possible bit conversion and sample rate are needed to 'capture' the
maximum amount of detail in the analog signal being fed, especially with a full bandwidth complex mix.
Your statement may also be true. And the resolution between the two statements boils down directly to masking theory! I
subscribe to the theory that there is inner detail in music or test signals which is audible below the noise floor of any system for a
considerable distance. Of course, it is not an infinite distance. At some point it becomes academic as your friend makes clear. For
example, in digital calculations, it has been shown that you can hear a 24 bit truncation below a 18-bit noise floor. Why? Because
the distortion has not been masked by the 18-bit noise. So--it boils down to how far down below the noise floor theory #1 is correct,
versus how far below the noise floor theory #2 is correct! Quite simple, eh? At what point the masking of the system noise covers
up the distortion caused by the reduced resolution. This can only be settled by psychoacoustic means, and ultimately by listening.
In the meantime, I suggest caution and conservativism, that is "the more bits, the better---probably".
So far, each time I increase the wordlength precision of my own work, I find an audible improvement. Yet at the same time, I have
not yet moved to a 24-bit A/D, because the sound of my custom-built 20-bit UltraAnalog A/D is superior to most any 24-bit A/D that
I've heard. There are currently a few 24-bit A/Ds which are a pinch better to my ears, but I am not certain if that is because they
are 24-bits or simply because their circuitry is more accurate, more euphonic, more detailed, less jitter, or any of the many other
possible influences for better sound where at that low level where it becomes impossible to separate out the reasons for "better".
And to repeat points I make elsewhere: this 20-bit question only comes up at the beginning and end of the chain, because when
you start processing (DSP calculations), more bits are definitely better.
Hope this helps,
Bob
------------------
Hi!
You're web site is a real gold mine of information. It can sound quite technical since I'm only starting out my little home DAW(on
a powerful Pentium II). I see I have a lot to learn and everything about mixing and especially mastering is great to read. I was
wondering what you thought about my plans (if you have the time to answer, even shortly). I see the new 24bits/96kHz
revolution and want to wait to have everything on my PC, from A/D to sound card, to internal processing (sequencer software
like Samplitude 2496 and also plugins) with this type of resolution. I have seen plugins frow Waves that use 56 bits internally
and dither down to 24 bits afterwards. I see that ADAT is creeping up slowly to 24bits, too. These are all the parts I want to
have on my DAW. What do you think about the quality level I could achieve on this setup? I know I'll have to research a lot for
each piece of equipment to be of very good quality but I have the time (about 2 or 3 years before final completion of what I
want) although not that much money (in the thousands but not tens of thousands...). Any advice would be appreciated. Thanks for your time and wonderful articles!
Hello. Thanks for your fine comments.
You know, it may seem funny coming from me, but my best advice here is don't get too hung up on the numbers...The engineers
who are most successful at using the toys you're describing....have put in many years of dues recording and mixing music the old
fashioned way. It's up to your ears and talent; weighs as much as the technical knowledge around here.
Yes, by all means follow as much of my continuing technical advice as possible. That advice is designed to keep you out of
trouble, but it's not a magic road to great sounding music. All those soundcards, and all that resolution and all those tracks don't
amount to a hill of beans unless you know how to put the tracks together to make a whole piece of coherent, beautiful-sounding
music.
In my opinion, the quality level someone can ultimately achieve by these numeric advancements will be more limited by talent and
ears than by the equipment. "24" is not some magic number that makes everything automatically better.
Now for a few technical comments: on the question of "24" it's also how the equipment works inside on its way to and from "24"
that will determine the quality of the sound. High internal precision is important, much greater than 24.
But let me clue you into a little secret. On the conversion end (A/D and D/A side), most so-called 24-bit converters contain 4-6 bits
or more of marketing hype. Mikes, preamps, converters, gain stages, and room noise contain enough energy to self-dither all but
the most pristine sources to less than 20 bits! "20" bits done right on the input and output ends of the entire process is more than
enough, as long as the processing in-between works with longer words.
24-bit signal to noise ratio on the input or output end, or just about anything greater than 19 bits, is equivalent to trying to detect a
candle that's a mile away, and in front of the sun, to boot. Most people have no idea how small a magnitude the LSB of 20 thru 24
bits is.
So, watch out for the marketing hype, use your talent, and go by the numbers as we talk about it here at Digital Domain. Sort of a
"More Bits Please" article with common sense attached!
Next point, the newer equipment you propose in your letter will actually present numerous challenges and problems, new ones
that I have barely touched on, from software bugs to ergonomic nightmares. "It won't be like this when we get the computer"---or
will it?
After you find the computer-based studio equipment that you think meets your dreams, expect to spend two-three more years
debugging it, and replacing half of it because the manufacturer didn't anticipate some of your situation. Your talent may find
workarounds for those problems, but can you wait that long? Consider working with the best you can now...make good music now
using traditional-based high-resolution tools, some of them computer based, but long established. There are plenty of examples of
"totally digitally mixed" albums currently released that sound absolutely horrid because someone "drove it all by the numbers"!
Best wishes,
Bob Katz
