PCM Fundamentals
What is Sampling?
This process converts a continuous-time analog signal into discrete-time samples before PCM encoding begins.
A speech signal has a maximum frequency of 4 kHz. What is the minimum sampling frequency required?
8 kHz (Nyquist rate).
A PCM system uses 8-bit quantization. How many quantization levels are available?
28=2562^8 = 25628=256 levels.
What is Encoding?
This PCM stage converts quantized samples into a sequence of binary digits for transmission.
What are 16 levels?
A PCM system uses 4 bits per sample. This is the number of unique quantization levels that can be represented.
What is the Nyquist Sampling Theorem?
This theorem states that the sampling frequency must be at least twice the highest frequency component of the signal.
What is 8 kHz?
If a voice signal has a maximum frequency of 4 kHz, this is the minimum sampling rate required to avoid aliasing.
What are Sampling, Quantization, and Encoding?
According to PCM generation, these are the three main stages performed after receiving an analog signal.
What is Quantization?
During PCM generation, this process assigns each sample to the nearest available amplitude level.
What are 256 levels?
An 8-bit PCM encoder can represent this many quantization levels.
What is Aliasing?
Engineers observe overlapping spectral components after sampling a signal at a rate below the Nyquist rate. This phenomenon is called ________.
What is Quantization Noise (or Signal Quality)?
A PCM system uses 7 bits instead of 8 bits for encoding. This design choice primarily affects this performance parameter.
What is 1101?
A quantized sample is assigned decimal value 13 in a 4-bit PCM encoder. Write its binary code.
What is 64 kbps?
A PCM system samples a signal at 8 kHz and uses 8 bits per sample. Determine the bit rate of the transmitted PCM signal.
What is an Anti-Aliasing Filter?
This component is placed before the sampler to remove high-frequency components that could cause aliasing.
What is the Sampling Stage?
A communication engineer notices distortion in the reconstructed signal because the input signal was sampled below the Nyquist rate. Identify the stage where the problem originated.
What is Amplitude Discretization (Quantization)?
A PCM transmitter consists of an anti-aliasing filter, sampler, quantizer, and encoder. If the quantizer is removed, what key function of PCM generation is lost?
What is at least 300 Hz (or slightly higher in practice), based on the Nyquist criterion?
A biomedical engineer must digitize an ECG signal with a maximum frequency of 150 Hz. To ensure accurate reconstruction, determine an appropriate minimum sampling frequency and justify the choice.
What is 120 kbps?
A PCM system samples at 12 kHz and uses 10 bits per sample. Calculate the resulting bit rate.
What is Reduced Quantization Error and Improved Signal Quality?
An engineer doubles the number of quantization levels while keeping the sampling frequency constant. Analyze the effect on signal quality.
What is System B, because higher quantization levels reduce quantization error and improve signal fidelity, though at the cost of increased bandwidth?
Two PCM systems are proposed for a smart-city sensor network: System A uses 8-bit quantization and System B uses 12-bit quantization. Considering bandwidth and signal fidelity, evaluate which system is preferable for high-accuracy monitoring.
What is a PCM system using 8 kHz sampling and 8-bit quantization (64 kbps), providing acceptable voice quality with efficient bandwidth utilization?
A telecommunications company wants to transmit speech signals over a bandwidth-limited channel. Design a PCM system by recommending suitable sampling frequency and number of quantization bits while balancing voice quality and transmission bandwidth.
What is System B because more quantization levels reduce quantization error?
Two PCM systems are available for transmitting medical data. System A uses 8-bit quantization, while System B uses 12-bit quantization. Which system provides better signal accuracy and why?
What is increasing the number of quantization bits, since it reduces quantization noise while Nyquist requirements are already satisfied?
An engineer can either increase the sampling rate or increase the number of quantization bits to improve signal quality. Which choice is more effective when aliasing is already eliminated?
What is a PCM system with an 8 kHz sampling frequency and 8-bit quantization, producing a 64 kbps bit stream?
Design a PCM system for transmitting speech signals with a maximum frequency of 3.4 kHz while maintaining good voice quality and efficient bandwidth usage. Specify a suitable sampling frequency and quantization resolution.