difference in reference levels with different ad/da converters

[subatomic]

If this is in the wrong forum, I apologize. It's confusing the hell out of me and I just need some help.

I recently started using a Fireface. I'm using a Tango24 on one of the adat i/o.
My problem is that with both units set to +4dBu reference level, and a test tone sent to both an analog input on the Fireface and on the Tango, The Fireface input meters show the Fireface signal to be approx. 6dB hotter than the Tango input.
On output, I get the reverse. Same signal sent to Fireface and Tango outputs. Tango output is approx. 6dB hotter than Fireface output.

I dragged out the manual for the Tango 24 converters. I thought that I'd compare the specs of the two units' analog sections.

here's what I found:

A/D
Tango lists "headroom" at 15dB. (maximum level 5dBV at -10dBV reference level, or 19dBu at +4dBu reference level)

Fireface shows maximum level (0 dBFS) @ Lo Gain: +19dBu, @ +4dBu: +13dBu, @ -10dBV: +2dbV

D/A

Tango lists "headroom" at 15dB. (maximum level 5dBV at -10dBV reference level, or 19dBu at +4dBu reference level)

Fireface shows maximum level (0 dBFS) @ Hi Gain: +19dBu, @ +4dBu: +13dBu, @ -10dBV: +2dbV


it definitely looks like the Hi Gain and Lo Gain specs from the Fireface match up with the +4dBu specs on the Tango. That would be consistent with what I've found in testing. With Fireface at +4dBu, I observed an approximate 6dB difference between the Fireface and Tango. This would seem to be consistent with the specs.

It seems that if I operate the Fireface at Hi Gain output and Lo Gain input, that the levels (and specs) match the Tango 24. Is there any drawback to operating at these levels? The manual isn't exactly clear what those levels are even for.

I don't believe that either converter has options for calibrating input and output levels. Maybe this is a sign that this doesn't belong in High End?

Can anybody help?

[subatomic]

anyone?

[subatomic]

ok...

maybe someone can point me in the direction of another forum where I could get some help with this??

I know that there are people here with the knowledge I'm looking for. What gives? do I stink?

[subatomic]

the same tone played back through both an analog output of the Fireface and an output from the Tango24 I get 6dB hotter output from the Tango.

the same tone played into both an analog input of the Fireface and an input of the Tango24 I get 6dB hotter input from the Fireface.

the specs of the two units (listed above) seem to indicate that this is normal. but, I have to admit that I don't completely understand the specs, so I'm trying to find out if I'm completely misunderstanding them.

thanks for responding!

[lucey]

Assuming the meters are equal (or very close) and both are reading a 0dbfs as a max:


If you play a tone (say 1k @ 1.25V AC) into and out of a single unit you should get the same level (voltage, or volume) at the DA as the input ... yes?

If so, each is calibrated to itself, at a different reference level. If one of them has a trim, tweak it on the AD to match the other ... AND the DA the same level.

So if the tango needs to go up 6db on Input to match, then take it down 6db on it's output, so the signal path is even level unto itself.


Then you can use either unit with any signal you record ... otherwise you need to stick with the same converter in and out or levels will be off.

[subatomic]

Originally Posted by lucey

Assuming the meters are equal (or very close) and both are reading a 0dbfs as a max:


If you play a tone (say 1k @ 1.25V AC) into and out of a single unit you should get the same level (voltage, or volume) at the DA as the input ... yes?

If so, each is calibrated to itself, at a different reference level. If one of them has a trim, tweak it on the AD to match the other ... AND the DA the same level.

So if the tango needs to go up 6db on Input to match, then take it down 6db on it's output, so the signal path is even level unto itself.


Then you can use either unit with any signal you record ... otherwise you need to stick with the same converter in and out or levels will be off.

apparently, each IS calibrated to itself, at a different reference level.
unfortunately, neither has a trim.

but, in addition to the +4dBu and -10dBV reference levels, the RME does have a "lo gain" input and "hi gain" output setting. this seems to decrease the input by approx. 6dB and increase the output by approx. 6dB.

with this setting, the two units are very close to matched.

I'm assuming that the RME has the better converters. Am I making a sonic sacrifice using the RME with these settings?

[lucey]

Originally Posted by subatomic

apparently, each IS calibrated to itself, at a different reference level.

Makes sense ...

unfortunately, neither has a trim.

No software trim in 1db steps or an internal trim pot?

but, in addition to the +4dBu and -10dBV reference levels, the RME does have a "lo gain" input and "hi gain" output setting. this seems to decrease the input by approx. 6dB and increase the output by approx. 6dB. with this setting, the two units are very close to matched.

good ...

I'm assuming that the RME has the better converters. Am I making a sonic sacrifice using the RME with these settings?

no, nothing to worry about ... it's an analog stage change, no big deal to the sonics and even if it were it's a small price to pay for having interchangable converter paths

[subatomic]

thanks a ton!