Converting pro audio signal (1.23v) to consumer line level (0.31v)?

[cbdb]

sorry just read your last post and if the meters read dbu there not the ful scale meters most digital gear comes with. Any source of test signal? Pro gear is designed to run at +4dbm (0VU) nominal signal. If your meters are in dbm(dbu) a music signal should sit between +4 and +8 dbu on the input whitout going over. This should maximize your S/N and still leave enough headroom.

 

[cbdb]

sorry again Are you saying your output meters only reach -30dbu??? Then Im confused. I thought your outs were too high and you wanted to pad them? This is too low and maybe your +4 -10 switch affects the outs also, which should get rid of your problem?

 

[steve71]

if your going out of a -10 dbm unbalanced out of your pre into a +4dbm ballanced ins to the dbx do you have enough input gain on DBX to make up the 14 dbm? This maybe where the grainyness is comming from. What kind of meters are on the dbx? Full scale (the max meter reading is zero, this is where you run out of bits and headroom) Then you need to know the operating level; what meter reading do you get when you input a +4dbm (1.23v??) signal. It should be around -20db Full scale. This is also your head room. when you feed the dbx unit from your pre, your signal on the meters should be bouncing around this level.

The Driverack PA has a +4/-10dbu switch on the back which I've set to -10dbu. My preamp has plenty of gain to drive the input side of the DBX.

I guess the meters on the dbx are non standard

Here's a picture of the unit.
http://cachepe.samedaymusic.com/med...kpafront-753757302c765419e16d1694c11f3ad8.jpg

sorry just read your last post and if the meters read dbu there not the ful scale meters most digital gear comes with. Any source of test signal? Pro gear is designed to run at +4dbm (0VU) nominal signal. If your meters are in dbm(dbu) a music signal should sit between +4 and +8 dbu on the input whitout going over. This should maximize your S/N and still leave enough headroom.

No source for a test signal, but it seems logical to assume that the red led (+22dbu) indicates clipping, correct?

sorry again Are you saying your output meters only reach -30dbu??? Then Im confused. I thought your outs were too high and you wanted to pad them? This is too low and maybe your +4 -10 switch affects the outs also, which should get rid of your problem?

Yes my output meters are only hitting -30dbu. The trouble is that (1) anymore than -30dbu is too loud and (2) -30dbu on the outputs is giving poor d/a performance. I want to pad down the 6 outputs on the dbx (after the d/a conversion) such that I can hit +10/+15dbu on peaks (as per the threshold LEDs), but still achieve a reasonable volume.

 

[cbdb]

you are correct about more output, this unit is also EQ ,compressor etc make sure this stuff is all bypassed to start. And your right (sorry just thought of this) this unit is made to work at zero out wich will drive your amps into full power so you need a "volume control" before the dbx, your preamp. lower the input, its 24 bit so it should be OK

 

[Burnedfingers]

Quote:

The DBX doesn't clip until it hits +20dbu acording to the input leds. Unless I'm missing something +10 to +15dbu on peaks is ideal, no? Everything I've read on the subject states that you want to set up your gain so you maximize the resolution of your A/D & D/A converters (without clipping). Most feel that you're even better off using a 6ch volume control after the digital X-overs D/A conversion.

Ok, first off don't trust the led's or any analog meter. They are there for a rough estimate of what is going on. The proper way to set up the device is with test gear. Input a signal and adjust to have all pieces clip in the signal chain at the same time.

The specifications on this device say 24bit and it should remain 24 bit processing regardless of the level input and or output. The grainey sounding is a result of improper setup. I have used Shure DFR22's in applications and have NOT hit the input hotter than 0db with absolutely no problems. I have used other DBX products and have not hit the input hard and haven't suffered sonically.

 

[cbdb]

and yes do add the T resistor pad on the outputs; 15 db should work

 

[steve71]

Thanks again for all the help guys. I built up a L pad on a breadboard to test things out. My Trends Audio chip amp is unbalanced and running the show from 500-7khz so I figured it'd be a great place to run a test.

Using a 100ohm shunt resister and 5K ohms R1 in series gets me in the ball park volume wise but I think a little less attenuation would be better. I'll buy some more resisters and experiment. As far as impedance matching goes the dbx has an output impedance of 120ohms. I couldn't find the input impedance of the Trends Audio chip amp, but power amps tend to be in the 10-47kohms range, so 5k is a little low

So with that in mind my L pad isn't impedance matched. I didn't notice any change in tonality (the side effect of incorrect impedance matching?) but IIRC some of the other pad configurations should provide a better impedance match.

As far as sound goes there was a significant improvement in sound over the 500-7k range. More hall/reverberation sound, better separation of voices and a less homogenized sound stage.