Chapter 1: Balanced and Unbalanced Signals

Question 1

What are the features of a balanced system/cable

Answer 1

Two conductors and a Shield (Ground/Earth)

Question 2

What is the function of each pin on an XLR cable?

Answer 2

Pin 1; Ground/Earth. Pin 2; Positive (hot). Pin 3; Negative (cold).

Question 3

‘TRS’ stands for what…?

Answer 3

Tip Ring Sleeve

Question 4

What is the T, R and S for a TRS jack?

Answer 4

Tip; Positive, ring; Negative, Sleeve; Earth

Question 5

If Equipment/cables have different configuration of pins (e.g. 2 is negative and 3 is positive), what happens to the signal.

Answer 5

The (absolute) phase is inverted.

Question 6

How many degrees will the ‘phase invert’ button on a console flip the phase by?

Answer 6

180 degrees

Question 7

Describe the basic benefits of a balanced cable?

Answer 7

They can reduce noise and interference which improves the SNR and the fidelity of the signal

Question 8

‘SNR’ stands for what…?

Answer 8

Signal to Noise Ratio

Question 9

How does a balanced cable reduce the noise?

Answer 9

it inverts the Polarity of the signal travelling through one of the two wires in the cable.

Question 10

Where does the polarity inversion take place?

Answer 10

In the amplifier circuits at the beginning and end of a balanced cable.

Question 11

How is the noise actually cancelled out?

Answer 11

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.

Question 12

What are the features of an unbalanced cable?

Answer 12

One conductor and a Shield (Ground/Earth)

Question 13

Can a TS (Tip-Sleeve) or Phono cable carry a stereo signal?

Answer 13

No, it is the two pins (XLR) or Tip and Ring (1/4” Jack) that allow stereo signals to be carried.

Question 14

What is the difference between ‘consumer’ and ‘professional’ audio cables/equipment?

Answer 14

Consumer- Often Unbalanced and have higher impedance (resistance) so they run at lower line levels/voltages.

Question 15

What do unbalanced (‘line-level’) signals operate at a strength of?

Answer 15

-10 dBV (usually 1/4” TS Jack or Phono (RCA) connectors and single/dual core cable)

Question 16

A balanced line-level signal operates at …?

Answer 16

+4 dBu (usually using 1/4” TRS jack or XLR connectors and dual core cable)

Question 17

What logarithmic voltage ratios are used for (1)professional? and (2) consumer products?

Answer 17

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)

Question 18

What is the dB difference between balanced Professional and unbalanced Consumer gear?

Answer 18

11.78 dB/ 12 dB (although this can vary depending on the system set up)

Question 19

Give an advantage of having a 11.8 dB better SNR in a balanced (+4 dBu) cable?

Answer 19

• 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.

Question 20

How could you overcome the problem of distortion when using +4dBu output to a -10dBV input?

Answer 20

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).