Chapter 1: Balanced and Unbalanced Signals Flashcards
To understand Line level and Audio fidelity through SNR and Cabling
What are the features of a balanced system/cable
Two conductors and a Shield (Ground/Earth)
What is the function of each pin on an XLR cable?
Pin 1; Ground/Earth. Pin 2; Positive (hot). Pin 3; Negative (cold).
‘TRS’ stands for what…?
Tip Ring Sleeve
What is the T, R and S for a TRS jack?
Tip; Positive, ring; Negative, Sleeve; Earth
If Equipment/cables have different configuration of pins (e.g. 2 is negative and 3 is positive), what happens to the signal.
The (absolute) phase is inverted.
How many degrees will the ‘phase invert’ button on a console flip the phase by?
180 degrees
Describe the basic benefits of a balanced cable?
They can reduce noise and interference which improves the SNR and the fidelity of the signal
‘SNR’ stands for what…?
Signal to Noise Ratio
How does a balanced cable reduce the noise?
it inverts the Polarity of the signal travelling through one of the two wires in the cable.
Where does the polarity inversion take place?
In the amplifier circuits at the beginning and end of a balanced cable.
How is the noise actually cancelled out?
The noise in a cable occurs equally on both the original and inverted signal. This means that when the inversion is reversed, the two signals become perfectly in phase, but the noise signal will be 180 degrees out of phase and is therefore removed.
What are the features of an unbalanced cable?
One conductor and a Shield (Ground/Earth)
Can a TS (Tip-Sleeve) or Phono cable carry a stereo signal?
No, it is the two pins (XLR) or Tip and Ring (1/4” Jack) that allow stereo signals to be carried.
What is the difference between ‘consumer’ and ‘professional’ audio cables/equipment?
Consumer- Often Unbalanced and have higher impedance (resistance) so they run at lower line levels/voltages.
What do unbalanced (‘line-level’) signals operate at a strength of?
-10 dBV (usually 1/4” TS Jack or Phono (RCA) connectors and single/dual core cable)
A balanced line-level signal operates at …?
+4 dBu (usually using 1/4” TRS jack or XLR connectors and dual core cable)
What logarithmic voltage ratios are used for (1)professional? and (2) consumer products?
Consumer uses decibel volts/dBV (reference voltage; V0= 1.0000 volt 0 dBV)
Professional uses decibels unloaded/dBu (reference voltage; V0=0.775 volt 0 dBu)
What is the dB difference between balanced Professional and unbalanced Consumer gear?
11.78 dB/ 12 dB (although this can vary depending on the system set up)
Give an advantage of having a 11.8 dB better SNR in a balanced (+4 dBu) cable?
- It will not pick up noise in areas of strong radio frequency or hum fields
- Longer cables can be used without picking up as much noise.
How could you overcome the problem of distortion when using +4dBu output to a -10dBV input?
Use a pad to attenuate the level, use the +4/-10 switch that is a common feature on many pieces of equipment or use a DI (if connecting unbalanced equipment to balanced equipment).
