To -db pad or not to pad?

Patryk_Rebisz

Patryk_Rebisz

Veteran
Recently we built a new system (MC 6.5 with AJA Kona3 card). The audio comes out of the card digital thus it needs to be converted into analog. We were give a free M-Audio Flying Cow box. However the audio i get through that set-up sounds much hotter then what i used to get with USB box. Thus my question is: should i pad -10 or 20 db the audio or should i simply turn down the audio on my mixer?
 
You did not reveal where the audio is going that seems too hot? Why is it not adjustable at the input of the destination? A complete picture allows us to offer more compatible and comprehensive responses. Generally speaking, it would be better to adjust the analog levels rather than compromising the digital levels.

Note that the XLR connectors have the higher professional output level of +4dB. While the 1/4" connectors have the consumer output level of -10dB. You also did not mention what USB box you were using before, but it seems likely it was -10dB.
 
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Here is more info:

Old set-up
Computer > U-Phong UFO202 > 1/4 cables > Eurorack UB502 > 1/4 cables > speakers
(for proper volume the dial was set at 1/3 of Eurorack's dial)

Current set-up
Computer (with AJA Kona3 card) > 24bit Flying Cow > 1/4 cables > Eurorack UB502 > 1/4 cables > speakers
(for proper volume the dial is set at 1/4 or 1/5 of Eurorack's dial)
 
Thanks for the additional information, but it is still not clear why the level isn't adjustable at the (still unidentified) speakers?
Good for you that you recognize that running the UB502 at "1/4 to 1/5" is not very optimal and is an indication that levels are not right along the chain.

The UB502 appears to have only one channel with a "GAIN" control (which accomodates anything from consumer -10dB to pro +4dB).
In the absence of details we presume that you are using the stereo line inputs. Unfortunately Behringer doesn't really reveal what the sensitivity of these inputs is. They only say: "The stereo channels are designed to handle typical line level signals." Not particularly helpful when "line level" has such a wide range of definition. And there is no GAIN control on those stereo "line level" inputs.

This seems like a gain-staging question. The next step in your chain is to ask where are the LED indicators on the UB502? Are they showing a proper signal level without being too low (down in the noise) or too high (clipping and distorting)? And we are assuming that the digital output is operating at "normal" levels and you aren't trying to monitor 100% compressed head-banging heavy metal or something?

And we come back to the question again, what speakers and what kind of adjustment do you have there?
 
Richard thank for the info. Here is more:

Speakers are Tannoy Revela 501a - right now the trim is at around 1/4 of its ability.

Because the only thing that has changed in the set-up is AJA card and the digital-to-analog converter (Flying Cow) i assume that the issue is somewhere with those 2 devices.
 
Yes, basically, it seems like the output from the Flying Cow is significantly greater than from the UFO202.
Google can't find any information about "U-Phong UFO202" so we don't know what its output rating is.
The 1/4 inch outputs from the Flying Cow are rated for -10dB which SHOULD be compatible with the line-level inputs of the UB502.
But you didn't answer the question about the level indicator LEDs on the UB502?
I agree with you that 1/4 seems like the lowest reliable setting for sensitivity of the speakers.
It may be that you need some fixed pads, but there are still too many unknowns in the signal path.
Please confirm exactly which input and output connectors you are using on the UB502.
Also please reveal exactly where all the controls are set on the UB502, and what the LED indicators say.
 
Eurorack UB502 manual
5http://portal.tugraz.at/portal/page/portal/Files/zid/files/manuals/verleih/Behringer.pdf
According to the Behringer manual, both the main balanced XLR and unbalanced Ctrl. Room 1/4" out have a max. level of +22dBu which usually makes the nominal level +4dBu. I would suggest using the Behringer's XLR out to the Tannoy's XLR in. I assume the Tannoy 1/4" input is the same config. TS or TRS. In that configuration you should not need a pad...
The only trim adj. I see on the Tannnoy, is for HF EQ comp.
 
The Tannoy Reveal 501a has a "VOLUME" potentiometer, and a "HF TRIM" 3-position slide switch below it.
It has a rated input sensitivity of "0.775V RMS for full output" which puts it sensitive enough for consumer -10dB, and rather over-sensitive for pro +4dB.
Using a +4dB output (such as the Behringer UB502 XLR outputs) may make matters worse,
although the Tannoy documentation suggests that there is no difference between the 1/4 inch input and the XLR input.

We still don't know how the gain is staged through the UB502, so still not clear whether pads are needed, or just proper control settings (and cables).
 
Exactly which input connectors are you feeding the audio into?
Exactly which output connectors are you using to feed the speakers?
Exactly WHERE are EACH of the controls on the UB502 set? (CRITICAL!)
When you are playing audio through the system which LEDs are lighting up on the UB502, and how often? (CRITICAL!)
Can we assume that you know how to read an LED "VU meter"?
Are you using native 1/4 inch connectors on each of these cables and NOT any kind of adapters (like XLR to 1/4 inch)
Is there really something called "U-Phong UFO202"? Seems very strange that Google never heard of it.
Details are important here. Don't blow them off.
 
It is never recommended to have the mix control turned up for any channel you aren't using.
That is just asking for trouble and the source of additional noise.
Turn all the way OFF the "1 LEVEL" control and the "2/3 LEVEL" control.

It appears that when you are playing a -20 dB tone out of your computer, the UB502 is properly indicating -20dB on the LED meters.
What did the UB502 LEDs read when using your old setup?
It seems very strange that a -20dB signal out of the UB502 is generating such a loud signal in your monitor speakers.
You could put some pads in there and that would remedy the symptom.
But that would not satisfy me. I still believe there is some other fundamental problem here.
You don't answer specific questions very well, so it is difficult to diagnose this at such a distance.
 
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