Help with A/D conversion Please!

C

chace

New member
Hey guys Need help ahhh! I have a grasp on it but would like some more info what is a A/D converter why would you use one and how does it work, please answer in point detail.

I have a mbox Heh heh and I think I am losing quality on the converion as the input signal sounds great but what is being played back after recordings definetly as reduced quality not that it sounds bad or anything just not a excellent replication of the input signal.

Please help
 
As the name suggests A/D converters take your analog signal and convert it into a digital one.

If you want to use a digital device (computer, digital multitrack etc.) to record, process, edit, store your audio then you need A/D converters. If you want to send that same audio back out to analog gear (to monitors or a tape recorder etc.) then you'll need D/A converters. The Mbox has both (as you probably know).

How do they work? a detailed answer is probably a bit out of my league but in simple terms they turn your analog signals in to 1s and 0s so the digital device can interpret and reproduce the signal.

You can get better quality converters than are in the Mbox but they should easily be good enough so that you don't hear any obvious degradation in the audio following conversion.

I suspect your problem lies elsewhere.

Elaborate a bit on your set up, your recording process/chain and the exact nature of the problem and someone might be able to help.
 
Are you plugging the mic directly into the m-box? If so,how are you monitoring the input, if not through the m-box? I'm with Kevin, the m-box doesn't have terrible convertors. You shouldn't hear a drastic change in sound quality just because of them.
 
Hmmm.. the mbox's converters and preamps are fine- you're problem is elsewhere.

Make sure your recording levels are good (almost clipping red at the loudest parts, but not.) You can have a very loud sound by cranking your mix control over towards "direct" (or whatever the label is) while recording but not actually have a good level going to "tape" - set by the 2 gain knobs at the top.

Then check the mix control on your mBox- the one that goes between playback and the direct signal. If you have that set wrong (i.e. too much towards direct signal during playback) your recorded tracks will sound very quiet.

Also, the direct inputs are hard right and left- unless you hit the MONO button. Then the inputs are mono, but the playback from pro tools will still be in stereo. If you are recording in stereo, don't forget that you then have to pan the recorded tracks right and left as they typically default to mono if you are using 2 mono tracks to record your 2 inputs. Stereo track default to wide panning.

Just some ideas.
-Chris
 
thanks guys for all your help I will try draw up a scenero ok. I have avalon U5 DI wich I put my taylor through I also have fostex pm2 for monitoring. Ok I get my self nice warm signal but stay conservatively below the red as digital clip meter arent that reliable. Now I pan left for input(direct) so I dont hear the delay sounds sweet than I stop recording pan right (playback) and listen to what I have recorderd, still sounds good all I can say is I love quality and I can here the loss of info yes I also listen to tracks in stero. I sample at 24 bit and think aroud 96 or 88.2khz or something like that (bounce at 44.1khz).

if you say you should hear no loss in quality, than why do they make better outboard converters and why do people use them to improve their recording's. I want to capture my input signal best I can what is the point of having good outboard gear if you losing some quality on your medium. I have had a look at a A/D conv by crane song looks good.

I am also going HD(high def) Hope the 192 conv are good
thanks guys you are legends

Rock on
Pep
 
Crane Song makes good stuff, so does Lavry. You do really have to spend thousands of dollars to get a noticeable improvement in convertors.
 
chace said:
thanks guys for all your help I will try draw up a scenero ok. I have avalon U5 DI wich I put my taylor through I also have fostex pm2 for monitoring. Ok I get my self nice warm signal but stay conservatively below the red as digital clip meter arent that reliable. Now I pan left for input(direct) so I dont hear the delay sounds sweet than I stop recording pan right (playback) and listen to what I have recorderd, still sounds good all I can say is I love quality and I can here the loss of info yes I also listen to tracks in stero. I sample at 24 bit and think aroud 96 or 88.2khz or something like that (bounce at 44.1khz).

if you say you should hear no loss in quality, than why do they make better outboard converters and why do people use them to improve their recording's. I want to capture my input signal best I can what is the point of having good outboard gear if you losing some quality on your medium. I have had a look at a A/D conv by crane song looks good.

I am also going HD(high def) Hope the 192 conv are good
thanks guys you are legends

Rock on
Pep
Click to expand...
I can't comment on high end converters because I don't use them. I use a prosumer card (M Audio delta 1010LT) and when I go from analog into digital there is no noticeable degradation in the audio. A-D conversion isn't exactly irrelevant but there are other things which I would place higher up the list of importance when it comes to sound quality (room, instrument, performance, mics, pres etc).

Dan lavry (who makes very high quality converters himself) wrote a paper some time ago on sampling rates:

http://www.lavryengineering.com/documents/Sampling_Theory.pdf

he concluded that there's no benefit recording above 44.1khz at all, in fact he went as far as to say:

"Sampling audio signals at 192KHz is about 3 times faster than the optimal rate.
It compromises the accuracy which ends up as audio distortions."

So really high rates are actually a bad thing.

I think the quality of converters are more important than the sample rate you record at.

Word length/bit depth is different, the consensus seems to be that 24 bit is better than 16 bit.
 
chace said:
I sample at 24 bit and think aroud 96 or 88.2khz or something like that (bounce at 44.1khz).

if you say you should hear no loss in quality, than why do they make better outboard converters and why do people use them to improve their recording's.
Click to expand...

First, the Mbox can only do 44.1 and 48kHz so you aren't really sampling at the higher rates even if your software says you are. If you are using pro tools it won't even let you try, but other software might. If your software is set for a higher samplerate somehow, that could be part of the problem- or all of it.

As for "no loss of quality"- of course there is a loss of quality. Using a mic will sound different than using your ears, and your preamps, room, convertors all affect the over all quality that your are going to get. The convertors and preamps in the mbox ($450us) are not going to make your tracks sound bad, but they aren't going to sound as clean, open and accurate as an Apogee Rosetta (around $2000us). A soundblaster card or the built-in ins and out of a computer will make your tracks sound bad.

If you are talking about Pro Tools HD, then yeah the convertors on the 192 interfaces are pretty sweet. But for the price the had better be! And even they don't compare to the Rosetta. Its all a trade off: how much can you afford vs. what level of quality do you need. If you learn to use that mBox well, most of the average listeners won't be able to tell the difference.

Take care,
Chris
 
Chris Shaeffer said:
First, the Mbox can only do 44.1 and 48kHz so you aren't really sampling at the higher rates even if your software says you are. If you are using pro tools it won't even let you try,.

Its all a trade off: how much can you afford vs. what level of quality do you need. If you learn to use that mBox well, most of the average listeners won't be able to tell the difference.

Take care,
Chris
Click to expand...

Thanks chris and your right I am sampling at 48khz I am not at home so could not check what I was sampling. But wanted basically to say that it was not my sample rate causing the recording to be of less quality than the input. as you know you can here the input signal when you pan left on input, I want what I record to be like that, thats all

Thanks Kev that article was pretty informative I would really like to know what sound engineers and the people who make the 192khz stuff think about that. Dont know if I could accept that so easily as I am more of a operator rather than a technician. kev I was just talking about the input quality vs the recording quality that I am getting regardless of what gear or room I am using

well this thread has taught me heaps thanks all of you for your help
 
I'm with Dan Lavry (and I use his converters). I think recording and processing in 24 bit is a very cool place to be, but I tend to record at the target frequency (in most cases, 44.1kHz, or 48kHz for video projects).

I've had discussions with engineers on the topic before on several occasions - "Why do you bother recording at such high sample rates when you don't really hear the difference?"

After beating it to death more than once, I came to this brilliant conclusion: It takes away any excuses. The band can't bitch about the sound because "they were recorded at a lower rate than Studio (?) uses" or something.

A lot of the high-samplerate hype is market-driven. Gear is touted sporting high rates, and people want it because "in theory, it might sound better" even though in many cases, all it does is take up more disk space.

I do a fair amount of orchestral recordings - Normally, straight to a Masterlink recorder. As it's undoubtedly going to pass through an analog mastering chain, I usually just set the rate at 96kHz. Why? The deck sounds good there. IMHO, 99% of the time, it sounds just as good at 44.1kHz also. Arguably BETTER at 44.1 with better converters.

My own personal conclusion? 24-bit, at the target rate, with the best converters you can get your hands on. If you can't get a good sound with that, there's something else wrong.
 
I've used an Mbox. I thought it sounded a little better than other products in its price range but not much. I've found the EMU 1820m to be impressive.

Good D/A often improves the situation. You might try the Lucid DA9624 or the Kurzweil Rumour.
 
You don't really need to record with a higher sampling rate of 44.1 unless you're using mics that record higher than 22.5k, like earthworks TC30s or something. Bit rate should always be 20 or 24 bit to avoid jitter.
 
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