Can anyone enlighten me:
I get very different output levels from my preamps into recorders depending on an ADAT or Line level analogue signal.

Scenario: Live festival stage: x16 mic splits (x2 ARTS8 splitters) from Soundcraft desk into: ISA828 & Audient ASP008 pre's.

Each preamp outputs x8 analogue line level into a Fostex DV2424LVmk2 digital recorder (24 bit/44.1)
and also x8 ADAT (24 bit) into a Yamaha AW2400 multi-track recorder, recording at 16 bit (i forgot to switch jumper in ISA to force to 16 bit and venue mud and wet was not place to open it up..)

The main recorder in this case is the Fostex (files go to client on CF card) so i worked with a regular -12dB or just over max level. This is set on the pre's as there is no input control on the fostex.

The ADAT levels coming into the AW were significantly lower. The AW was recording at 16 bit/44.1 so i would have liked a slightly higher level. This is my back up recorder this time but i also mixed a live disc from it (stereo to HHB recorder) and i worked on a mix at home from the AW to add to the package for the client (just in case they like it)
i had to use lots of make up gain to get decent levels.

Is there any reason that the ADAT is lower in level or have i missed a link in the chain?

cheers

steve

This is a simple gain-structure question, but there aer many possible level anomalies when working with different converters and different analogue interfaces.

You need to find out what the actual operating levels are for the analogue line interfaces at the preamp outputs and at the recorder input that you are working with, and how they relate to 0dBFS (digital full scale). We need real numbers since the metering will probably also provide misleading impressions!

I think the ISA428 is set up so that +4dBu (standard line level) provides a digital output of -18dBFS. The Audient is the same: 0dBFS = +22dBu.

However, the obvious pragmatic solution is to set the preamps and recorders up again, input a test tone to the preamps and adjust the gain to achieve the desired digital level from their internal converters (say, -10dBFS to represent nominal peak level), then configure the analogue input sensitivity on the recorders to achieve the desired level via that path.

hugh


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Technical Editor, Sound On Sound

Quote sabletones:

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The main recorder in this case is the Fostex (files go to client on CF card) so i worked with a regular -12dB or just over max level. This is set on the pre's as there is no input control on the fostex.

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According to the Fostex website you can change the input sensitivity from a nominal +4dBu to -10dBv. If you have it set to -10dBv then that would probably explain the level difference.

James.

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JRP Music - Audio Mastering and Restoration.
http://www.jrpmusic.net

These guides much appreciated.

I went for pragmatic approach with concomittant homework on level relationships etc and attempting to relate spec's to practice.

Used o1v oscillator (omni outs +4dB balanced) to send -12dB tone to ISA pre line input, and yes the ISA -18 on meter is a +4dBu at line output.

I checked the fostex set up. I was already using a +4dB balanced level at line input. The unbalanced -10dBv did indeed shoot into the red, but i wasn't using that originally....but the observation got me deeper into the manual, thank you James.

Current solution is to adjust input levels on the AW2400 by using the input layer fader (needs to be +5 to equate to levels on preamps/fostex. i can increase the meter level here also with the virtual rotary level. I will ask Yamaha what the difference is here? I am doing this:
1) in an effort to understand
2) when i need more than x8 channels i can only record at 16 bit on the yamaha.

What i have not grasped yet is why the ADAT level from pre's into the AW2400 requires +5dB boosting to match level on fostex and ISa pre (audient being less visually precise)......all stages seem to be operating balanced +4dBu....etc. Maybe that's the way it is?...or is that a stupid thing to say?

I've got my tin hat on if i've been a bit slow on the uptake!

cheers
Steve