A/D and D/A conversion

[shivermetimbers]

I will try to stay on point with this as best I can.

 

We all know that we should strive to get the best conversion as technically (and financially) possible in and out of our computers.

 

So the questions deal with:

 

1.) How do you know the quality of the converter you are using?

Will depend on its application and what other equipment it is being used with? The ten-thousand dollar A/D converter is much better that a one-hundred dollar M-Box interface. So where is this spec info located to show this?

 

 

2.) What happens when one converted signal passes through another converter?

Using a Firewire, USB, PCIe cards should give a direct path to the HD should allow the high precise converted signal to go direct to the storgae place (hard drive). Right/Wrong? For instance, you sing thru a high quality pre-amp/converter box, but you have no means to get the signal into the computer except for a low end interface?

 

3.) Does using the I/O utility insert plug in affect the conversion rate?

 

 

Aside form the argument of bit depth and bit rate (and financial cost), what are the best practices for getting the analogue info converted and sent into and out of the computer (storage device)? Sounds silly, but think about it for a minute.

[ski]

Hi Shiv,

 

You can't really trust the accuracy of published specs on almost any equipment, not just AD/DA's. Use what you read as a rough guide, not gospel. I have a tendency to read between the lines of published specs. For example, I read them with an eye out for what they don't mention. That can be telling as well.

 

Best way to compare AD/DA's is to have direct experience. Many years ago when I swapped out my MOTU 2408 (mk I) for an RME Fireface 800, I immediately noticed more clarity in the bottom end. It was like night and day. But there really wasn't much difference in the top end at all. So I called a golden-eared engineer friend who went through a similar upgrade path and he confirmed that most of the difference you'll hear in the better interfaces is clarity and definition in the bottom end, not so much the top end.

 

And now for a short yarn (arrrrr, matey). Recently I've had the need to run Logic on two computers simultaneously. So I brought my old MOTU back into service on my old G5. And now with many years of being used to the sound of the FF800 under my belt, the MOTU sounds a tiny bit duller than the FF800 though the difference isn't vast by any stretch.

 

Of course, how much detail you can hear, either in the high or low end, is going to be shaped by other factors such as the quality of your monitor controller (if any), power amps and monitors. But to sum it all up, the best way to tell if an AD/DA is better than another is by direct comparison.

 

Next...

 

When signal is processed through the A/D side, the data will be written directly to your hard drive, though it will likely be routed through some kind of driver software (bridge). I'm not aware of any intermediate processes that result in an indirect path to writing data to the hard drive, nor one that would adversely affect the sound or the integrity of the data.

 

Can't address your third question because I never use the I/O utility.

 

HTH,

 

Ski

[Eric Cardenas]

1. These are the specs my AD (line in):

 

• Resolution AD: 24 bit

• Signal to Noise ratio (SNR): 110 dB RMS unweighted, 113 dBA

• Frequency response @ 44.1 kHz, -0.1 dB: 10 Hz – 21.5 kHz

• Frequency response @ 96 kHz, -0.5 dB: 5 Hz – 45.5 kHz

• Frequency response @ 192 kHz, -1 dB: 5 Hz – 66.5 kHz

• THD: < -110 dB, < 0.00032 %

• THD+N: < -104 dB, < 0.00063 %

• Channel separation: > 110 dB

• Maximum input level: +19 dBu

• Input: 6.3 mm TRS jack, electronically balanced

• Input impedance: 10 kOhm

• Input sensitivity switchable to Lo Gain, +4 dBu, -10 dBV

• Input level for 0 dBFS @ Lo Gain: +19 dBu

• Input level for 0 dBFS @ +4 dBu: +13 dBu

• Input level for 0 dBFS @ -10 dBV: +2 dBV

 

SNR and THD are what I mostly look at.

But that is not going to tell you how the AD sounds!

 

2. I'm not sure I understand the question?

Do you mean if using an external converter?

 

That means that you are bypassing the converter in your interface so no AD will take place.

 

3. No! Why should it?

[David Nahmani]

1.) How do you know the quality of the converter you are using?

A/B testing. Specs don't tell you anything, and having worked in a lab that makes those specs for high end hi-fi speakers and the likes, I've seen how easy it is to make specs say just about anything you want them to say. Don't trust the numbers.

 

2.) What happens when one converted signal passes through another converter?

Not sure I understand that question: an A/D converter converts an A(nalog) signal into a D(igital) signal. And you can't "pass" that digital signal "through" another A/D converter (which expects an Analog signal at its input).

 

Using a Firewire, USB, PCIe cards should give a direct path to the HD should allow the high precise converted signal to go direct to the storage place (hard drive). Right/Wrong?

An interface's sole purpose is to transmit a bunch of zeros and ones to a DAW software, whose sole purpose is to place those zeros and ones into a computer file named "audio file", correct. The signal chain is:

 

Sound -> Transducer (mic) -> Preamp (mic preamp) -> A/D converter -> interface -> computer.

 

Goes without saying that at the lower end of the price range, "interfaces" actually incorporate some of those elements, for example most low end interfaces have integrated A/D converters, many have integrated mic preamps, and some even have integrated mics (Apogee one).

 

So as long as the interface works properly, it does not affect the sound quality of your recording. As long as the DAW works properly, it does not affect the sound of your recording. The only devices that affect the sound of your recording are the mic, the mic preamp and the A/D converter.

 

For instance, you sing thru a high quality pre-amp/converter box, but you have no means to get the signal into the computer except for a low end interface?

Assuming the low end interface works properly and doesn't drop signal or loses bits in the transmission or have clocking issues, it won't affect the quality of your recording, correct.

 

3.) Does using the I/O utility insert plug in affect the conversion rate?

How do you use the I/O insert plug-in? For what? I don't see how it comes into this conversation.