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Questions and Answers
What is the primary purpose of companding in a communications system?
What is the primary purpose of companding in a communications system?
- To improve the dynamic range of a communication system (correct)
- To eliminate the need for sampling
- To reduce signal noise during transmission
- To convert analog signals directly to digital signals
How does the analog companding process begin?
How does the analog companding process begin?
- Through the insertion of diodes in the analog signal path (correct)
- By converting a PAM signal directly into PCM code
- Using a linear compression approach for all signals
- With the expansion of the received signal
What effect does increasing the value of μ have on compression characteristics?
What effect does increasing the value of μ have on compression characteristics?
- It results in a linear curve.
- It increases the compression. (correct)
- It decreases the compression.
- It maintains constant SQR.
Which two companding methods closely approximate a logarithmic compression function?
Which two companding methods closely approximate a logarithmic compression function?
What is the minimum dynamic range required for voice transmission?
What is the minimum dynamic range required for voice transmission?
In which regions is μ-law companding predominantly used?
In which regions is μ-law companding predominantly used?
What value of μ is required to achieve a relatively constant SQR and a 40-dB dynamic range?
What value of μ is required to achieve a relatively constant SQR and a 40-dB dynamic range?
When working with an eight-bit PCM system, what μ value is commonly used?
When working with an eight-bit PCM system, what μ value is commonly used?
What happens to high-amplitude signals during the companding process?
What happens to high-amplitude signals during the companding process?
To restore signals to their original proportions in the receiver, what process is employed?
To restore signals to their original proportions in the receiver, what process is employed?
What is required for voice quality telephone signals concerning compression ratio?
What is required for voice quality telephone signals concerning compression ratio?
In A-law companding, how does the SQR compare to μ-law companding?
In A-law companding, how does the SQR compare to μ-law companding?
What is the result of compressing a 50 dB analog input signal to 25 dB prior to transmission?
What is the result of compressing a 50 dB analog input signal to 25 dB prior to transmission?
What is the overall circuit gain when combining compression and expansion factors?
What is the overall circuit gain when combining compression and expansion factors?
What constitutes the final stage of the analog companding process in receivers?
What constitutes the final stage of the analog companding process in receivers?
If the maximum input voltage is given as 4 V, what happens to the compressed output voltage?
If the maximum input voltage is given as 4 V, what happens to the compressed output voltage?
How many codes are present in each subsegment of segment 7?
How many codes are present in each subsegment of segment 7?
What is the maximum magnitude of error introduced during the companding process?
What is the maximum magnitude of error introduced during the companding process?
What does the decoder do to the truncated bits in the companding process?
What does the decoder do to the truncated bits in the companding process?
What value does the decoder logically guess for the truncated bits in segment 6?
What value does the decoder logically guess for the truncated bits in segment 6?
What causes the quantization error in segments 0 and 1?
What causes the quantization error in segments 0 and 1?
What is the resolution used in the given analog sample voltages?
What is the resolution used in the given analog sample voltages?
What is the output of the companding process when the original voltage is exactly matched?
What is the output of the companding process when the original voltage is exactly matched?
In segment 5 and segment 7, how many bits are used in each code after companding?
In segment 5 and segment 7, how many bits are used in each code after companding?
What is the primary characteristic that differentiates A-law companding from μ-law companding?
What is the primary characteristic that differentiates A-law companding from μ-law companding?
In a digitally companded PCM system, what occurs in the transmitter after the analog signal is converted to a linear PCM code?
In a digitally companded PCM system, what occurs in the transmitter after the analog signal is converted to a linear PCM code?
What compression level is used in the most recent digitally compressed PCM systems?
What compression level is used in the most recent digitally compressed PCM systems?
How many segments are typically represented in a μ255 algorithm's compression curve?
How many segments are typically represented in a μ255 algorithm's compression curve?
What happens to the bit positions marked with an X in the μ255 encoding table during compression?
What happens to the bit positions marked with an X in the μ255 encoding table during compression?
What characteristic best describes the expansion process in the receiver of a digitally companded system?
What characteristic best describes the expansion process in the receiver of a digitally companded system?
What format constitutes the 8-bit compressed PCM code in the digital companding algorithm?
What format constitutes the 8-bit compressed PCM code in the digital companding algorithm?
In the digital companding process, how is the slope of each successive segment characterized?
In the digital companding process, how is the slope of each successive segment characterized?
What constitutes the quantization error in digital companding?
What constitutes the quantization error in digital companding?
In the worst-case scenario, how do quantization and compression errors behave?
In the worst-case scenario, how do quantization and compression errors behave?
In which segments is there no compression error?
In which segments is there no compression error?
What is the formula to calculate the percentage error introduced by digital compression?
What is the formula to calculate the percentage error introduced by digital compression?
Why is the maximum percentage error consistent across all samples in segments 2 to 7?
Why is the maximum percentage error consistent across all samples in segments 2 to 7?
What can be inferred about the behavior of quantization and compression errors in segments 2 through 7?
What can be inferred about the behavior of quantization and compression errors in segments 2 through 7?
What is the worst possible error in segments 0 and 1?
What is the worst possible error in segments 0 and 1?
What leads to the increase of the encoded voltage from 0.32V to 0.33V?
What leads to the increase of the encoded voltage from 0.32V to 0.33V?
Study Notes
Companding
- Companding is a process used in digital communications to improve the dynamic range of a signal. It encompasses two steps: compression and expansion.
- Compression reduces the amplitude of high-amplitude signals, while expansion increases the amplitude of low-amplitude signals.
- This process helps in maintaining a consistent signal-to-noise ratio (SQR) throughout a wide dynamic range.
Analog Companding
- Analog companding involves compressing the analog signal before it is converted to a digital format. This is achieved using specialized diodes in the signal path.
- During transmission, the compressed signal is sampled, quantized, and encoded into a linear pulse-code modulation (PCM) code.
- In the receiver, the PCM code is decoded, filtered, and expanded back to its original dynamic range.
- The process of companding is essential for transmitting diverse signals, like voice, music, and video.
μ-Law Companding
- Popular in the United States and Japan, μ-law companding is a specific type of analog companding.
- The compression curve for μ-law is nonlinear, with a steeper slope for lower amplitude signals and a shallower slope for higher amplitude signals.
- The parameter 'μ' determines the level of compression. A higher 'μ' value results in greater compression.
A-Law Companding
- Used in Europe, A-law companding is another type of analog companding.
- A-law features a slightly flatter SQR compared to μ-law for a given dynamic range.
- However, A-law tends to be inferior to μ-law in terms of noise performance for low-amplitude signals.
Digital Companding
- In digital companding, the compression happens after the analog signal is converted to a linear PCM code.
- Expansion occurs before decoding in the receiver.
- Digital companding offers advantages like improved efficiency and flexibility.
Digital Compression Error
- Digital compression introduces minor errors due to the truncation of bits during the compression process.
- The maximum percentage error due to compression is uniform within each segment. Notably, segments 0 and 1 have no compression error due to the linear nature of those segments.
- Understanding compression error is essential for ensuring accurate signal reconstruction in the receiver.
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Description
This quiz explores companding, a crucial process in digital communications that enhances signal dynamic range through compression and expansion. It covers analog companding techniques and the μ-law companding method used in various applications. Test your understanding of these concepts and their significance in signal transmission.
