Re: GAIN STRUCTURE

[van Sinn <vansinn@post.cybercity.dk>]

Rick Walker wrote:
> froshsizzle wrote:
> "It's possible all levels match just fine, but also possible that some 
> instrument-level input is connected to a lineout level."
> 
> Will someone please explain the difference between instrument level,   
> lineout level and mic level
> and why it is important that these levels match each other (viz a vis,  
> noise in your signal chain)?
> 
> I'm never quite understood this.
> 
> Which one is +4?    Which one is -10?
> 
> Which of these creates less noise and why?
> 
> Thanks..................
> 
> 
> still perplexed,    Rick


Thy shall be relieved.. :D

I'll try to explain from a practical point of view.
Standards do exist, but are by far adhered to.
Professional (studio) equipment often adhere to standards; out beloved 
musicians gear often vary quite a lot.

Even so, it's not really a major problem, as long as we read the manuals 
and understand which in/outputs are at which levels.


Instrument inputs:
Alway high-inpedance, often around 100-500Kohm, but can be anything from 
20Kohm to 1Mohm (1Mohm mostly seen in older tubeamps).
Levels can vary from -50dBu to -10dBu, but are often stated as -10dBu.


Line inputs:
Always (somewhat) low impedance, i.e. from a few 10th of ohms to the 
often used 600ohm standard (which can be seen both with balanced and 
unbalanced connections).
Levels can vary quite a lot, but are often stated as +4Bu.


Impedance:
Must either match or the diving device output impedance must be 
significantly lower than the next device input impedance.

Balanced circuits are most often 600ohm.  If both outputs and inputs are 
i.e. 600ohm, it's called impedance matching.
In this case no signal losses will take place, and there will be no 
reflections, provided the correct (600ohm) cables are used.

If the driving device is low-impedance, say 1-10ohm (or even 600ohm), 
and the next device is high-impedance, say 10-100Kohm, all will be well.

The low-impedance output circuitry will have no trouble driving cables 
et al.. and the next device's high input won't present any significant 
load.
In the reverse case, i.e. output impedance not low enough and input not 
high enough, signal reflections make take place.
I'll refrain from further elaborating on this, as most all our devices 
are designed just fine WRT output and input impedances.


To summerize:
As long as using single-ended connections, i.e. non-balanced, most all 
our gear will behave WRT impedance, so it's mostly a matter of knowing 
which inputs and outputs are designed for which signal levels.

Manuals can be pretty useful..


-- 
rgds,
van Sinn