The digital transmission of speech may be represented using the block diagram of [Figure 6.1]. (a) Part of the signal at point P on [Figure 6.1] is shown in [Figure 6.2]. The analogue-to-digital converter (ADC) samples the signal at time intervals of 0.25 ms. Each sample is converted into a four-bit number with the smallest bit representing 1.0 mV. Use [Figure 6.2] to determine the four-bit number produced by the ADC at time (i) 0.25 ms, (ii) 1.25 ms. (b) The digital number is transmitted and then converted to an analogue form by the digital-to-analogue converter (DAC). Use data from [Figure 6.2] to draw, on the axes of [Figure 6.3], the output level of the DAC for time t = 0 to time t = 1.50 ms. Assume that there is no time delay of the transmission of the signal between point P and the output of the DAC.

1. (a)(i)0.25 ms, number ................................................................................................[1]
2. (a)(ii)1.25 ms. number ................................................................................................[1]
3. (b)Use data from Fig. 6.2 to draw, on the axes of Fig. 6.3, the output level of the DAC for time t = 0 to time t = 1.50 ms. Assume that there is no time delay of the transmission of the signal between point P and the output of the DAC.[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.