Jimmie Eadie Lecture

Question 1

What happens if two identical audio signals are combined but one is polarity-inverted

Answer 1

They will cancel each other out, leading to phase cancellation and silence

Question 2

What happens if you invert the polarity of a signal played in isolation

Answer 2

Won’t notice a change

Question 3

What does inverting the polarity of a signal mean?

Answer 3

Means flipping the waveform upside down

Question 4

What’s phase?

Answer 4

The time-alignment of sound waves or signals

Question 5

When two waveforms are out of phase, what happens?

Answer 5

They can partially or completely cancel each other out when mixed together, affecting the clarity and fullness of the sound.

Question 6

What does comb filtering create?

Answer 6

Create a hollow sound, and in sever cases, it can significantly reduce clarity and intelligibility

Question 7

Explain sum and difference processing

Answer 7

Refers to a matrix process where two signals are added together (sum) to create a mono signal or subtracted from one another (difference) to create a stereo signal with enhanced spatial effects.

Question 8

When would you use an FIR filter?

Answer 8

When phase linearity is important

Question 9

When would an IIR filter be important?

Answer 9

When computational effiency is prioritised

Question 10

What is the impact of microphone spacing on sound quality

Answer 10

When two microphones are placed at different distances from a sound source, the sound arrives at each microphone at slightly different times

Time difference due path difference -> phase cancellations when signals are combined = comb filtering

Mixed together, phase differences can cause constructive and destructive interference

Question 11

What is the rule of thumb for microphone placement

Answer 11

The distance between microphones should be at least three times the distance from each microphone to the sound source

Question 12

What is a better arrangement in terms of microphone placement

Answer 12

To place two microphones in the same physical space

Does not suffer from any phase issues because the capsules are in the same point and space and hence time.

Question 13

Explain how noise cancellation works

Answer 13

1. Incoming ambient sound
2. Sound is picked up by microphone and sent to noise cancellation circuitry
3. Noise cancellation circuitry inverts wave and sends it back to headphone speaker
4. Original ambient sound and new waveform cancel each other out