Generate a +4 signal from audio interface?

[samplebias2]

I should probably own one but I don't have a signal generator. . . is there a way to send out
a signal at +4 for (like a sine wave from a software synth) from an audio AD/DA (I have an RME USB Babyface Pro)?

I have a tube limiter I put out of calibration by trying to center the gain reduction meter, the 1-man design team
named the "gain reduction" adjust and "METER ADJUST" pots backwards IMO.

Instructions for calibrating seem easy:

"-Meter knob set to input with +4 signal adjust metr adj to zero

-Meter knob set to GR adjust to zero set it between 500 and 1000hz"

 

[ccaudle]

is there a way to send out
a signal at +4 for (like a sine wave from a software synth) from an audio AD/DA

Sure. A dedicated software program that will generate levels calibrated in the digital domain would be preferred to a synthesizer, since it is not as likely that a synthesizer would have carefully controlled output levels.
You could also use a sine signal from a test CD (if you still have one of those), or generate one with e.g. Octave and save as a wave file. REW (Room EQ Wizard) can generate sine waves, that is a common measurement software the people on this forum often use.

Do you have a decent voltmeter to verify the analog output level? If not the Babyface has a mode which limits the output to +4dBu, you could generate a sine wave just reaching 0 dB FS and put the Babyface into +4 mode, and the output should be pretty close to +4 dBu.
Or you could leave the output in +19 mode and generate a sine wave at -15 dB FS, that should also be pretty close to +4 dBu.
Either way it would be good to verify with an accurate voltmeter that the output is at 1.23V.

 

[Chrisfromthepast]

+1 REW, and everything else.
If using a cheapo multimeter for AC measurements, you will likely get more precision if you set your sine freq at 60hz. Only this freq to test voltage, come back to the recommended frequency range for the compressor calibration.

 

[samplebias2]

Thanks, I'm going to try and execute these plans! Sadly the repair place in my area doesn't do quick easy repairs like this at the counter, seems like this could be done entirely under 5 minutes.....

+ETA I do have a voltmeter I should be able to check with

 

[pucho812]

You have an interface, you have a daw of some kind? I have yet to see a daw not able to generate a sine wave at level and frequency you want.
While I do use an audio precision regularly I also use logic the daw. This is because I can generate drummer (logic soft synth) which is awesome for doing final testing on a unit after it’s been fixed. Nothing like showing a client in real time your unit is working by using real drum tones.

 

[Tubetec]

I have an old Iphone who's only job in life now is as a signal generator,
I make Wav test tone files in Reaper with phase reversed L/R to form a balanced signal ,
I can precisely adjust the level to +4 with the multimeter .
Needless to say all services and communications with the Apple mothership are terminated ,
Easy to carry alongside the multimeter in the pouch , gives a very stable repeatable output signal with no chance of ground loops .

Neat idea to use drum samples to check gear is working .

 

[john12ax7]

I like the idea of repurposing an old phone. But I would think there are apps for signal generators? Would be a little easier than transferring wavs. Although probably wouldn't have the balanced out capability.

 

[ccaudle]

But I would think there are apps for signal generators? ...Although probably wouldn't have the balanced out capability.

This app lets you flip polarity on a per-channel basis, so should do the same thing:
https://ee-toolkit.com/audio-function-generator/

 

[samplebias2]

I've been using Cubase since forever but all for in the box production, I'll snoop around in menus I never look at . I got that REW program installed, I see a definite learning curve!

 

[samplebias2]

Sure. A dedicated software program that will generate levels calibrated in the digital domain would be preferred to a synthesizer, since it is not as likely that a synthesizer would have carefully controlled output levels.
You could also use a sine signal from a test CD (if you still have one of those), or generate one with e.g. Octave and save as a wave file. REW (Room EQ Wizard) can generate sine waves, that is a common measurement software the people on this forum often use.

Do you have a decent voltmeter to verify the analog output level? If not the Babyface has a mode which limits the output to +4dBu, you could generate a sine wave just reaching 0 dB FS and put the Babyface into +4 mode, and the output should be pretty close to +4 dBu.
Or you could leave the output in +19 mode and generate a sine wave at -15 dB FS, that should also be pretty close to +4 dBu.
Either way it would be good to verify with an accurate voltmeter that the output is at 1.23V.

I only see a reference in the RME manual to +4/-10 for the INPUTS. . . sounds like you're saying I can raise the output gain of a sine
till it measures 1.23V? If this caveman can figure out what XLR pins to put the leads on this might just work. I'll have to call the guy up and ask where the actual input GAIN knob on the limiter should be during all this

 

[scott2000]

RME has/had? a page with a bunch of different sine and noise wavs you can just plop on an audio track and adjust levels to fit?....

Ethan Winer had a nice little tool on his site for this as well... I need to find the name...not sure if it's still around//

here it is....

NTI virtual minirator.....

https://realtraps.com/info.htm
virtual minirator

 

[ccaudle]

I only see a reference in the RME manual to +4/-10 for the INPUTS

Sorry, I was confusing with the USB Babyface Pro FS, that seems to be one of the differences between the original Babyface Pro and the newer FS variant.

sounds like you're saying I can raise the output gain of a sine
till it measures 1.23V?

Yes, 1.23V is +4 dBu.

If this caveman can figure out what XLR pins to put the leads on

Pins 2 and 3 are the signal output pins.
Drawing of pin positions

 

[samplebias2]

This is why I come to learn from you smart people, hope some rubs off on me - thanks!!

 

[Tubetec]

I found the Iphone with a handful of preset wave files very adequate , typically I create a wav file thats +4db output at full volume on the phone , then you can easily attenuate the signal using the volume control . Its not even steps as you reduce the volume but it is very repeatable and accurate .

I looked at the Minilyser app but you still need to calibrate your interface everytime you want to use it ,either way lugging a laptop and interface around as a signal source is cumbersome .

 

[Graham Nystrom]

1.23V AC just in case there is any doubt in anyone's mind. Don't set your meter to DC. Audio is a a small AC signal over the hot and cold pins of your XLR or TRS. Steve Sadler taught me that one. And I think maybe Randy Blevins taught him that.

 

[scott2000]

1.23V AC just in case there is any doubt in anyone's mind. Don't set your meter to DC. Audio is a a small AC signal over the hot and cold pins of your XLR or TRS. Steve Sadler taught me that one. And I think maybe Randy Blevins taught him that.

shhh...
this takes some of the fun out of calibrating and troubleshooting

 

[shabtek]

RMS

 

[fallout]

Great advice has already been given but if you ever need a dedicated signal generator for your studio you can look for an old "Neutrik Minirator MR1". I bought one a while back for less than $100, it works great and I use it often.