Compare Series, Ladder, and Shunt Type Stepped Attenuators
In 1995 Goldpoint Level Controls began offering Ladder type stepped attenuators to audiophiles worldwide. And in 1998 we added the Shunt and Series type stepped attenuators.
But in 2003 we ceased building "Ladders" and "Shunts" because we found a way to make  stepped attenuators which had all of the audiophile positive attributes and none of the negatives. This entailed building Series type stepped attenuators using truly transparent sounding precision resistors. These specially selected resistors are thin film nichrome SMD type, laser trimmed to 0.1% tolerance. We now use them on all of our standard Mini-V stepped attenuators.
-Series Type Stepped Attenuators
As its name implies, the series type stepped attenuator is simply a series of  resistors forming one "long" voltage divider.  The rotary switch is used to select where, in this voltage divider, the output will be. Electrically, it is just like a potentiometer with built-in mechanical detents.
Like a potentiometer, the input impedance of a series type stepped attenuator remains constant, so the signal source always sees a constant, non varying load.
advantages:
    Only one switch contact in the signal path. 
    Fewer parts and lower cost than Ladder type.
    No "pops" or "clicks".
    Easier to use - emulates potentiometers.
-Ladder Type Stepped Attenuators
In a ladder type stepped attenuator, the rotary switch is used to select an input-to-output resistor and an output-to-ground  resistor, forming a set voltage divider for each switch position.
The total series resistance of each two resistor set is equal, so the signal source always sees the same impedance. Ladder type stepped attenuators minimize the effects of using less precise or noisy resistors. 
    Two switch contacts in signal path. 
    Often causes “pops” or “clicks" while turning knob.
    Twice as many resistors required
       (compared to series and shunt types). 
    Requires higher cost switches with twice as many wafers.
-Shunt Type Stepped Attenuators
In a shunt type stepped attenuator, a voltage divider is formed with one “constant value” input-to-output resistor, and one other resistor selected by the rotary switch position.
 
Although behaving just like a ladder attenuator for each switch position, shunt attenuators vary the impedance as seen by the signal source. To minimize this, one wants to choose a large value input-to-output resistor. This can conflict with the need to have a small  input-to-output resistor so that the attenuator will pass the maximum signal level at high volume settings (and have less effect on high frequency signals). 

This type of attenuator is best used with low impedance signal sources, thereby minimizing the effects of the  attenuator’s own varying input impedance and allowing a smaller value for the input-to-output resistor.
    Varying input impedance requires careful 
       consideration of the actual circuit and/or equipment 
       it will be used with so as to avoid impedance
       mis-matches with the signal source equipment.