The main aim of this project is to demonstrate the pulse code digitization and companding on a signal and to observe the effects of sampling depths and companding on the signal to noise ratio (SQR).
PCM- In the pulse code modulation (PCM), the signal is a digitally represented analog signal in which the signal magnitude is sampled with uniform intervals. Each sample is quantized to the closest value of the digital signal. In the pulse code modulation, the signal is binary. The two possible states represented in PCM are logic 1(high) and logic 0 (low). The main advantage of PCM signal is that it is derived from analog signal which is multiplexed with data from the computer and carried over a common high-speed channel.
COMPANDING- The combination of compressing and expanding is known as companding. In companding, the data is compressed before it is sent and then expanded at the receiving end using the same non-linear scale. The noise and crosstalk levels at the receiver are reduced due to companding. It is used in wireless microphones for better dynamic range and also in digital and telephony systems for compressing of the input signal and expanding of the output signal.
The below figure 1 shows the demonstration of PCM with and without companding.
Figure1- PCM with and without companding
Procedure to create PCM and companding on excel sheet
The PCM and companding of a signal is done on a spreadsheet using excel. Firstly, a sine wave is created by varying the time with respect to the amplitude. The frequency of the signal is taken as 10 Hz. The quantization process of the signal will be done. A quantized sine wave is then created. Now the number of levels cell (N) should be created. We take the value ...
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...ude=0.1, large N=8.
GRAPH I) Plot of SQR vs Amplitude with Companding (mu=255) and without Companding (mu=0).
GRAPH J) Plot of SQR vs bit depth both with Companding (mu=255) and without Companding (mu=0). Where A=1, and bit depths are 2, 4, 8, 16, 32, 64, 128, 256.
This lab was carried out to compand and quantizes a voice signal. We
In the Using the pulse modulation technique, the analog signal is converted into the digital signal. The process of quantization and companding of a signal is carried on the spreadsheets. To attain a clear signal to quantization noise ratio, the number of samples should be increased. By increasing the sampling depth, the quantization error can be minimized. By companding process, the quantization noise and distortion levels can be minimized. Companding improves response for low amplitude signals.
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