How to set the output level of A/D convertors

Johnrg

Johnrg

New member
Guys,

I have an ART mic pre amp that has a built in analog to digital convertor.

This has an output level dial that increases the level sent out of the analog outputs and the analog/digital convertor. I usually go out of this unit digital SPDIF into my workstations spdif, however this has it's own gain stage as well.

I have real trouble working out the correct setting for thhe input / output levels of these three things:

(1)Input Preamp=Analog VU meters
(2)A/D convertor=Rotary dial with digital meters
(3)DAW spdif input with input fader and meters.

Here's what I am thinking - can some one correct me if I am wrong:

Step one - DAW Spdif input - set this at unity gain (odb)

Step two - Pre Amp Analog VU input - aim for peaks at 0db (especially drums etc) the odd over is OK seeing it's analog at this stage.

Step three - A/D convertor output - increase this so my signal hits the DAW's input meters at average about -18db. Peaks maybe up to -6db.

How does that look?

Is there anyway I can send a test tone/pink noise into the mic pre to set the out level of the A/D convertor at the correct place so I never have to chage it once set?

Thanks for your help

JohnG
 
Are we talking about the ART Digital MPA? I love mine, anyway.

What I do is set the VU meter to "tube", which supposedly is a measure of tube stage level, with the red zone being into saturation zone. If you peg that meter, you'll get unpleasant distortion, so keep in between 0 and 3 for saturation, and lower for a cleaner sound. The tube level is set by the Input Gain and +20dB switch.

Then set the Digital Level where you need it for proper level, I shoot for half the LEDs lit, which is -12dBFS, lots of room for peaks there.

The Analog Output control is not in the SPDIF circuit.
 
I have an ART DPSII (dual channel tube with digital outs)

I suppose what I am trying to work out is the corelation between Odb on the VU meter and a similar setting on the A/D convertor.

How about running a test tone of some descrtiption like pink noise into the preamp and increasing it's gain till the meter shows a constant Odb and then setting the output A/D to hit my DAW at -18DFS. (bearing in mind that anlaog 0db's equivilent digital scale is about -18db)

Am I correct in thinking that I would then never then have to change the output level on the A/D convertor/preamp as it would always represent the input level from the inputted source ie a vocal peaking at 0db on the VU would always hit my DAW at -18DFS, If I pushed the preamp a bit then then out putted level would also increase as well to the stage where distorted input would basically equal distorted output.

Seems simple to me but I must be misunderstanding something.

JohnG
 
Johnrg said:
Seems simple to me but I must be misunderstanding something.

JohnG
Click to expand...

I think that's correct but I'm not sure that will always yield the best result. The second gain stage is a solid state stage that is fed to both analog and digital outs; the output gain controls operate as independent attenuators.

Thus if you set the digital output gain at a fixed level, then with a low level source, you will be forced to increase tube gain until saturation and then clipping, while you still have (clean) second stage gain to spare. As an alternative, you might want to increase tube stage gain to obtain saturation, which could require attenuation of the digital output stage to avoid clipping the converter.

Instead of using the VU meter as a digital meter, I would use it as intended, as a tube gain meter, and use the meters in your DAW to set the digital level.
 
OK, thanks for that. It's basically what I am doing now but I find it hard to keep nice even levels.

There always seems to be something that clips both on inputs and outputs.

I think maybe I am setting the output levels to high. If I aim for -18 on the digital input then this should catch the peaks. I can always ride the digital input fader when tracking vocals to give a bit more more presence in soft passages.

I have a tough time with the input VU. I go for peaks at Odb but always seem to have one note or one hit that sends the meter straight into the red and clips. If I lower the gain the presence seems to disappear.

I just think I am trying to track to hot.

Thanks

JohnG
 
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