LED VU meter guitar pedal

[Mailliw]

I think it would be cool to have a guitar pedal with a trimmable VU meter so I can match guitar levels before and after I switch on a different pedal.

Say I have a good volume with my distortion pedal on, I adjust a trim knob on my VU meter pedal to read 0 dB. Now I switch on my tremolo and the signal drops, so I switch on my boost pedal and adjust the volume so that my VU meter pedal reads 0 dB again.

Can a kit like this be modified with a trim pot so that I can adjust what its 0 dB reference is? From a typical electric guitar output to a hot signal coming out of a distortional pedal?

Thank you!

 

[sahib]

Did you take your playing into account? Output of your guitar varies with your playing.

 

[Mailliw]

When comparing levels, I can play a G versus a G, etc...

I'll try to read up more on the driver chip and see if I can figure this out on my own.

Thanks

 

[gemini86]

I can see where the cool factor comes in with a gadget like this... but I don't see it being musically useful. A good musician should be adjusting levels for what he/she wants to hear, or what will sound good- not trying to perfectly match every effect (maybe your phase shifter sounds better at a lower volume than your auto-wah or whatever else you want to think of as an example)

just my $.05 worth...

 

[Mailliw]

*Throws a nickel back at gemini* 

 

[JohnRoberts]

Something like that could help.. I would suggest making sure you use a slow average response detector circuitry since a lot of the loudness from fuzz effects are from squaring up the waveform, so peak levels would read similar or lower, while sounding louder.

JR

 

[lolo-m]

Most revelant would be a RMS indication... But the real problem is that even a RMS indication won't reveal the frequencies shape change that pedal can do... More distorsion means more high and mid-high (that are more agressive to your ears) and you feel a more loud sound with the same RMS level...
I do understand your wish, but it is maybe more complicated than it seams  :-\...

 

[JohnRoberts]

Most revelant would be a RMS indication... But the real problem is that even a RMS indication won't reveal the frequencies shape change that pedal can do... More distorsion means more high and mid-high (that are more agressive to your ears) and you feel a more loud sound with the same RMS level...
I do understand your wish, but it is maybe more complicated than it seams  :-\...

Do you have practical experience with RMS being more relevant for such an application? I am familiar the common thesis that RMS more accurately describes power content of a waveform, but I have done some direct comparisons between simple average and true RMS in a microprocessor based meter design I did, and using identical time constants for the RMS integration and simple average integration, I saw no visible difference with complex music.

Peak response will surely be misleading as it has almost nothing to do with perceived loudness. I don't expect enough difference (if any) between simple average and RMS to justify computing true RMS.

Note: Natural RMS attack/release characteristics (slightly faster attack than release versus average with same attack/release) does sound better for fixed time constant dynamics processors. For this guitar level meter the expense is not justified. IMO.

JR

 

[lolo-m]

I never say TRUE RMS... Analog Device have some simple chips to do the RMS to DC conversion... But certainly for this use, a simple diode bridge charging a RC network can do something similar... I'm not sure what would be cheaper...

 

[Gus]

First do some tests with effects like phasers and tremolos.  If you look at the peak to peak output you will note what sounds even to the uneffected sound is often > peak to peak.  Some have noted that corrections are needed maybe it could be as simple as trying it out first and writing down the % change etc between effects and using the notes to help with the VU reading.
  The way some effects "cut up" the waveforms and the ear brain might be more complex than RMS.  Also some Fuzzes compress the sound more than some distortions but if you look at the P to P it might be close, also the duty cycle can change the sound, % on both sides of zero crossing.

 

[Afarawayland]

First figure out the practical range signal wise of the guitar, once you know the highest of the high and lowest of the low you could then choose any of the LM391x chips.  Each has its differences. 

Know that the chips may have internal offset errors that will affect the accuracy with low signals (around 10-20mV level).

You could add gain to the signal and a account for the gain added in chip reference level circuitry.