2.1 Recording and Playback Flashcards Preview

As Physics Unit 1- Dr Bebb > 2.1 Recording and Playback > Flashcards

Flashcards in 2.1 Recording and Playback Deck (28)
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1
Q

What is an analogue signal?

A

Analogue signals are those which vary continuously with time.

2
Q

What is a digital signal?

A

Has discreet values.
A digital signal refers to an electrical signal that is converted into a pattern of bits.
The precision of the signal is determined by how many samples are recorded per unit of time.

3
Q

What are the stages in sound recording?

A

Sound waves cause a membrane in a microphone to vibrate.
These mechanical vibrations are converted- weak electrical signals- voltage mimics the displacement of air molecules by sound.
This signal is amplified.
Amplified signal fed into record head (electromagnet that produces magnetic field.)
The intensity of the field varies in the same way as the current (and therefore the original sound).

4
Q

Why and when is a mixer used in sound recording?

A

To balance the relative strengths of the signal if several microphones, or a series of microphones and guitar pickups are to be recorded together.

5
Q

What happens during playback of sound?

A

The tape passes the playback head where the tape’s magnetic field induces currents in this head.
These currents are amplified and the electrical signal is then passed to a loudspeaker where it is converted into sound by the mechanical vibrations of the loudspeaker cone or headphones.

6
Q

How is an analogue signal sampled?

A
  1. Signal voltage measured at regular time intervals.
  2. Measurement converted to a binary number.
  3. Digital number stored or transmitted to receiver.
  4. When sound is played again, binary data must be reconverted to analogue signal to drive loudspeaker.
7
Q

How does a digital signal processor work?

A
  1. Microphone produces an analogue signal, an ADC digitises it into binary.
  2. Signal sent to DSP, digital signal analysed and encoded using compression algorithm.
  3. Compressed data stored in memory.
  4. On playback, data retrieved from memory and decompressed.
  5. DAC changes digital value back to analogue voltage.
  6. Voltage applied to amplifier and speaker.
  7. Routine used in DSP is called codec.
8
Q

How is compressed data from a digital signal processor played back as sound?

A

Upon playback, the data is retrieved from memory and is decompressed.
A digital-to-analogue converter chages the digital values back to analogue voltage that is applied to the amplfier and speaker.
The routine used in the digital signal processor is called a codec for COmpression-DECompression.

9
Q

What is a common codec?

A

MP3.

10
Q

The more frequently an audio signal is sampled…

A

…the closer a regenerated wave will be to the original analogue waveform.

11
Q

What is the rule for setting out the minimum sampling rate of a regular signal?

A

It must be at least twice the frequency of the signal.

12
Q

What can happen if minimum sampling rate of a regular signal is not at least twice the frequency of the signal?

A

The regenerated signal can produce false sounds in what is called aliasing,

13
Q

What is quantisation?

A

The process of converting a continuous range of values into a finite range of discrete values.

14
Q

What is data compression?

A

A technique by which the same amount of data is transmitted by using a smaller number of bits.

15
Q

What is a digital filter?

A

A system that removes random noise from a signal or to extract useful parts from it.

16
Q

What are some advantages of digital signals?

A

Electromagnetic interference, signal loss and noise which effects signal quality, is virtually elliminated.
Digital data can be encrypted to provide some measure of protection against unwanted viewing/listening.
Digital data can be shared among many different devices.

17
Q

What does the faithfulness of a signal depend on?

A

The quantisation and compression used.

18
Q

What is one of the limitations to digital signalling?

A

Transducers usually generate analogue voltages which need to be sampled and then converted back to analogue at the end of the process.
Binary numbers cannot be heard from a speaker or seen on a number.

19
Q

Explain the effect that increased sampling rate and decreased quantisation levels has on the amount of storage required and the faithfulness of a digital signal.

A

Increased sampling rate leads to the amount of storage decreasing. The higher the sampling rate the more accurate the regenerated wave will be to the original sound but this means more storage is used.

20
Q

Suggest why a good compression routine will mean that a compressed signal will be practically indistinguishable from an uncompressed one.

A

It will have a smaller wavelength and a higher frequency so all the information is compacted into a smaller space so if there is a small error in the compression it will expand when you uncompress it- if there is little/no error the uncompressed wave will produce an accurate depiction.

21
Q

What is pulse code modulation?

A

changing analogue to digital
(analogue signal) is sampled
digital signal is (a sequence of) binary numbers

22
Q

Name and explain one type of compression technique.

A

lossy compression

loses physiologically unimportant info

23
Q

State an advantage of using compression when storing a digital video recording.

A

need to store less information
fewer bits
more films in same space

24
Q

State an advantage of recording music in an analogue form rather than a digital form.

A

Not losing any of the original signal detail.

25
Q

State an advantage of transmitting a signal using frequency modulation (FM) compared
with using amplitude modulation (AM).

A

Less susceptible to (e-m) noise/interference by e-m waves)
Easier to remove noise
Better quality since higher bandwidth/transmit more detail/higher range of frequencies in
signal
Less power wasted in carrier wave (more used in side band)

26
Q

State and explain advantages of digital data transmission compared with analogue.

A

Signal unaffected by noise
Multiplexing possible
More difficult to ‘tap’
Digital signals carry more information per second

27
Q

Describe and explain the purpose of modulation in a communication system.

A

Carrier wave
Frequency/amplitude modulation
By signal to be transmitted
Modulation enables more information to be transmitted.

28
Q

Explain why the use of a sampling frequency that is lower than the minimum sampling frequency could reduce the quality of the data received.

A

Higher frequencies will be lost.