line level to signal level

[rompelstilchen]

Hello,

I want to output the level of an audio card to the input of a guitar effect pedal

like this : guitar -> input of sound card ->[SOUND PROCESSING]-> output of sound card -> guitar effect

pluging the output of a steinberg usb audio card to my boss ds-1X pedal, once I engage the distortion I get an awfull noise that dont happen if I plug the guitar directly in the distro

I wanted to know if a simple resistor divider is enough or if I needed to use some sort of op amp circuit to buffer the impedance in anyway

I am not really good in analog electronic so I though maybe someone could give me clues

I found a lot of thing in google, they says so many different things that I get lost

regards

 

[d123]

Hi,

What sort of "awful" noise?

Not sure, have you got any numbers for members to work from if you know them/can find them? e.g. guitar max. and min output voltage > sound card max. (and min. "readable") input voltage > max. and min. input voltages for guitar effect/pedal. Others may provide a more knowledgeable description of what numbers are needed.

Couldn't say about op amp, sorry.

 

[barry]

I think your problem is that you're overdriving the effect. Guitar output level is on the order 50-100 mV peak. Line output is about 1V peak-10 to 20 times guitar output. So, you probably want to attenuate the output of the sound card. Guitar amps have a very high input impedance, and I would assume (but don't know for sure) that effects inputs are similarly high. Thus, you could probably get away with just a resistive divider.

 

[prairiedog]

Best to find out where the overload distortion is coming from. There are two possible places and you are probably overloading at both.

Guitar into a soundcard... MIC input or line input? You would be overloading the soundcard (mic) input. Try setting the guitar output very very low and listen on the monitors.

Boss DS-1X effects pedal is -20dBu in and out. A guitar is a much lower signal (than soundcard out) , which is what your Boss DS-1X effects pedal is expecting, than a PC sound card which has output line-level, -8dBu or 0.316V AC, which will overload the Boss effects pedal input.

I would run the guitar first into a pedal/pre-amp to get the signal up, then feed into the PC soundcard line input. The MIC input is too sensitive and noisy.
Then, the PC soundcard output is too much for the Boss pedal, but Boss has a level control which might cover that or not depending on Boss's circuit inside.

 

[rompelstilchen]

I think your problem is that you're overdriving the effect. Guitar output level is on the order 50-100 mV peak. Line output is about 1V peak-10 to 20 times guitar output. So, you probably want to attenuate the output of the sound card. Guitar amps have a very high input impedance, and I would assume (but don't know for sure) that effects inputs are similarly high. Thus, you could probably get away with just a resistive divider.

thx, I'll try that

- - - Updated - - -

Best to find out where the overload distortion is coming from. There are two possible places and you are probably overloading at both.

Guitar into a soundcard... MIC input or line input? You would be overloading the soundcard (mic) input. Try setting the guitar output very very low and listen on the monitors.

Boss DS-1X effects pedal is -20dBu in and out. A guitar is a much lower signal (than soundcard out) , which is what your Boss DS-1X effects pedal is expecting, than a PC sound card which has output line-level, -8dBu or 0.316V AC, which will overload the Boss effects pedal input.

I would run the guitar first into a pedal/pre-amp to get the signal up, then feed into the PC soundcard line input. The MIC input is too sensitive and noisy.
Then, the PC soundcard output is too much for the Boss pedal, but Boss has a level control which might cover that or not depending on Boss's circuit inside.

yes, I'll measure signals on the scope to be sure...but as I had read many things about impedance without really understanding that (complex/dynamic) part of a signal, I was'nt really sure if I needed some active reduction/buffer circuit

I'll first try to reduce the output

the card is a behringer (not steinber,my bad) uca222 https://static.bhphotovideo.com/lit_files/61860.pdf

Output impedance approx. 400 Ω
Max. output level 2 dBV

which is chinese to me, but at least it can handle the guitar input without beeing amplified (I do that in the processing part, a raspberry pi runing puredata)

some questions remain :

- why I had no noise when the pedal was in clean mode (off)

- I also have a tascam 2x2 and a audiophile 192 that I plug back directly to the amp using guitar rig 5 as a DSP, never had any trouble, guess the issue is becos of the input impedance of the boss pedal

-> if it works for a boss ds1x, will it work with all my other pedals or plugging it straight to the amp ?

- how do I figure the conversion ration from 2db to -20db ? I made some search and apparently db itself is a log ratio between input and output so I am a bit lost

regards

 

[barry]

2 dBv is 1.25v RMS.

when the pedal is in clean mode it's probably just bypassing all the circuitry. Some pedals still run the signal through some circuitry, while others completely bypass it.

dB is different than dBv. There is a direct conversion between dBv and volts. dB is just the ratio between ANY two signals, dBv is relative to 1v. In other words, 1V is 0dBv.

I'm not sure I understand your other questions. What do you mean about 'converting from 2dB to -20dB'? Do you mean you want to know how to reduce your signal 22 dB?

 

[rompelstilchen]

2 dBv is 1.25v RMS.

when the pedal is in clean mode it's probably just bypassing all the circuitry. Some pedals still run the signal through some circuitry, while others completely bypass it.

dB is different than dBv. There is a direct conversion between dBv and volts. dB is just the ratio between ANY two signals, dBv is relative to 1v. In other words, 1V is 0dBv.

I'm not sure I understand your other questions. What do you mean about 'converting from 2dB to -20dB'? Do you mean you want to know how to reduce your signal 22 dB?

22db ?

I mean to calc the resistors I would need to make a voltage divider

 

[barry]

Yeah, the difference between 2 db and -20 db is 22 db. Do you want to reduce your 2dBv signal to -20dBv? Simply find a table with dBv-to-volts conversion and calculate your divider from that.

 

[rompelstilchen]

Yeah, the difference between 2 db and -20 db is 22 db. Do you want to reduce your 2dBv signal to -20dBv? Simply find a table with dBv-to-volts conversion and calculate your divider from that.

thx

the actual formula is db = 20 log V

so if one needs the volts from db => 10 exp (db/20)

http://www.sengpielaudio.com/calculator-gainloss.htm

now I am going to try this