4 These are converted to electrical signals by (use) a microphone.

5. The information contained in the drum machine memory consists of (sample) of these electrical signals.

6. A drum machine contains (record) of sound taken at measured intervals.

7. This process is called (sample).

8. The functions of a drum machine include (pan) and (tune).

9. Panning means the (position) of the drum sound in stereo.

Word Study Compound nouns, 1

Study these examples of compound nouns and their meanings:

a silicon diode = a diode which contains silicon a smoke alarm = an alarm which warns of smoke a car radio = a radio for use in a car

Task 6 Explain each of these compounds:

1. a burglar alarm

2. a clock timer

3. a mercury switch

4. a car phone

5. a germanium diode

6. a ground wave

7. a block diagram

8. an assembly line

Some compound nouns have become single words, for example, a voltmeter -an instrument for measuring voltage. Explain the meaning of these words:

9 a fuseholder

10. awavemeter

11. a cellphone

12. headphones

13. an ammeter

14. a handset

Technical reading Sampling

Task 7

Read the text and answer these questions:

1. Is a sine wave an example of an analogue wave or a digital wave?

2. How many voltage levels does a digital signal have?

1. What is an ADC?

3. How frequently must an analogue signal be sampled when converting it to a digital signal?

4. What term means a 'binary digit'?

5. What effect do rounding errors have on a signal when it is converted back to an analogue form?

Fig. 1

Modern electronic circuits, however, often use digital signals because they can be processed more easily. The magnitude of a digital signal has only two levels, high and low, which can be represented by the binary digits 1 and 0 respectively (see Fig. 2).

1 1

1 1

_J

oo

0 0 0 0 0

00

00

00

о 0

Fig. 2

The analogue signals produced by transducers can be changed into digital signals using an analogue-to-digital converter (ADC).

10 Because the analogue signal is constantly varying, samples of the original signal must be taken at successive intervals of time. The magnitudes of the samples are changed into digital values by the ADC. This process is known as sampling (see Fig. 3).

The higher the frequency of the analogue signal, the more often it 15 must be sampled. However, it is usually adequate to sample a signal at twice its highest frequency.

Each binary digit used to show a binary value is known as a bit. The accuracy of conversion is limited by the number of binary bits used by the ADC. If the conversion is made using a four-bit ADC, only sixteen 20 different binary values can be produced. The smallest value is 0000 and the largest is 1111. If an 8-bit ADC is used, then 256 ( 2⁸) different digital values can be produced. When a measurement of the analogue signal does not coincide with one of these binary values, it must be rounded up or down (see Fig. 4).

1111 -

1110-

1Ю1H

1100-1011 -1010H 1001 -1000-0111 -0110-0101-0100-0011 — 0010-0001-I 0000­

this sample is rounded down

/

\

rounded up rounded down

\

Fig. 4

25 This leads to inaccuracies in the digital measurements. If the resulting digital signal is converted backto an analogue signal using a digital-to-analogue converter (DAC), these rounding errors will cause the analogue signal to suffer some distortion as shown in Fig. 5.

Fig. 5

Although low-quality transmission systems such as digital telephone 30 networks can operate successfully using 8-bit ADCs, it is necessary to use 12,14, or 16-bit ADCs in high quality music systems.

Audio recording systems

Tuning-in

Try to answer these questions:

What problems are there with records? What other recording systems are there? What do these abbreviations mean? a LP b CD

Read quickly through this text to check your answers to Task 1. Audio recording systems

For a long time hi-fi recordings have been produced on vinyl gramophone records. Records use an analogue recording system, which stores patterns by cutting a continuous groove in a vinyl disk. The shape of the sides of the groove represents the audio pattern. The 5 sound can be reproduced by spinning the record and using the movement of a metal needle in the groove to produce varying magnetic fields (see Fig. 1). These magnetic fields are then processed to produce the sound. A typical LP (long-playing record) has a recording capacity of about 45 minutes.

10 A digital recording system, known as a compact disc (CD) system, was introduced in 1982. This uses a laser optical mechanism in which a laser beam reads marks on the surface of a specially prepared perspex disc. It gives near-perfect reproduction of sound and the sound quality does not deteriorate with use. Some of the problems associated with