Fostex FR2LE gain staging

[dfuruta]

Long-time lurker, first-time poster here.

I recently purchased a Fostex FR2LE to use as a more portable solution for recordings where two channels will suffice; previously, I've had to lug around a desktop computer. The built in pres on the Fostex are ok, and the small size is very convenient. However, I'm confused about the proper gain-staging.

In addition to the gain controls for the pres, there's a "recording level" dial. I suspect this is post A/D conversion, but I can't figure out if it simply attenuates the signal or if it boosts as well. I would like for it to pass the signal with unity gain, but I'm having difficulty discovering from the (rather slow) built-in metering where this is.

So, for those of you with FR2LEs, how do you approach gain-staging? Do you leave the "recording level" wide open? Part-way up? Thanks for your advice!

[chris319]

My hunch is that the big recording level dial works in the analog domain.

When using the mic inputs I leave the big dial all the way open and set levels with the trims. When using the line input I use the big dial as the level control.

Watch out for the FR-2LE's outputs, though, both the line out and the headphone out. Past about 12:30 the output will clip on a 0 dBFS signal.

[dfuruta]

Thanks! Running it with the recording level full on was my instinct also. The outputs on the FR2LE are pretty awful. I noticed that as well.

[mathieujm]

Originally Posted by chris319

My hunch is that the big recording level dial works in the analog domain.

That's not right. This big knob works in the digital domain. It has a unity gain at appr 12:00.
The two little knobs adjust the mic preamp gain.
A good way is to put the big knob at 2:00 and then adjust the gain knobs to have a -12dbfs level for average level.
Then adjust the level knob.
An important thing to check is the two first leds on the left. They flash when the analog preamps overload.
The "over" leds flashes for digital overload.

JMM

[Thomas W. Bethe]

Originally Posted by mathieujm

That's not right. This big knob works in the digital domain. It has a unity gain at appr 12:00.
The two little knobs adjust the mic preamp gain.
A good way is to put the big knob at 2:00 and then adjust the gain knobs to have a -12dbfs level for average level.
Then adjust the level knob.
An important thing to check is the two first leds on the left. They flash when the analog preamps overload.
The "over" leds flashes for digital overload.

JMM

This is the way we set our FR2-LEs up for classical recording.

[chris319]

This big knob works in the digital domain. It has a unity gain at appr 12:00.

How did you come by this knowledge?

[mathieujm]

Originally Posted by chris319

How did you come by this knowledge?

When recording from line input, the gain knobs are inactive. So you can only digitally adjust with the level knob.
Using a source with a standart output level of -10dbV in the line input, you can adjust the level to obtain the same level than the source (gain 1). You will see that it's around 12:00.

JMM

EDIT : I just looked to Oade page about "How do I set levels on the recorder"
http://www.oade.com/Tapers_Section/faq-general.html#C1
And I don't understand this sentence : "This simple rule, using as little preamp gain as possible, will allow you to make the very best recording possible with your gear"

For me, the analog gain should give the highest signal possible without distortion to the AD converter. And if there is not enough analog gain, there will be some digital gain (with the level knob in the FR2LE or afterward in the daw) and I don't think it's the best practice to preserve the S/N.

[chris319]

When recording from line input, the gain knobs are inactive.

Those are for the mic preamps. With the line input the preamps are out of the circuit, i.e. the line inputs come in after the mic preamps.

So you can only digitally adjust with the level knob.

It could be doing this in the analog domain as well. It isn't necessarily the case that this has to be digital.

[mathieujm]

Originally Posted by chris319

Those are for the mic preamps. With the line input the preamps are out of the circuit, i.e. the line inputs come in after the mic preamps.

Yes, it's exactly what i tried to explain. It's the reason why you can calibrate the level knob using these inputs.

It could be doing this in the analog domain as well. It isn't necessarily the case that this has to be digital.

The fact is that le level knob is in the digital domain and when using the line inputs you can't adjust the analog gain.

Was I clear about the objective of what I described ? It was only to show that unity gain can be obtained with the level knob when it's positionned around 12:00.

JMM

[chris319]

The fact is that le level knob is in the digital domain and when using the line inputs you can't adjust the analog gain.

I'll ask my question again: How did you come by the information that it is in the digital domain? Did you ask Fostex or the Oade Brothers? Surely you have an authoritative source for this information. It is entirely feasible that there is an analog stage after the line inputs.

[mathieujm]

Chris, I asked to Oade about the gain and recording level stages. He answered me it is all analog. So my apologies !
I didn't ask him about the +12db introduced by the 1.30 firmware version
JMM
Posted via the Gearslutz iPhone app

[heva]

The +12dB option in v1.30 is working fine as far as I've found.
The mic-pre gain trims work very steep/fast between 4 and 5 o'clock, where I mostly need them, but it's way too much/awkward for my taste.

Using the +12dB , I can use the trims between about 12 and 3 o'clock, which seems to give more control over gain.

disclaimer: but I'm not a pro ...

[mathieujm]

Originally Posted by heva

The +12dB option in v1.30 is working fine as far as I've found.

I'll investigate more deeply this new option to see if the +12db change the noise figure. Because as you, I always have the trims between 3 and 5.
JMM