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64ET1405 Elec Net Principles

2. Topic 3 - Modems. The following MCQs are for use in the Modem lab/ tutorialMore than one answer may be correct . 3. 1. Wav files:. Are use to store video files on PCsAre standard files for audio in WindowsAre used for polyphonic tunes in mobilesAre a common file format used for UNIX . 4.

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64ET1405 Elec Net Principles

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    1. 64ET1405 Elec & Net Principles Topic Three: Testing your knowledge of Modems- Lab MCQs Updated 08 Nov 2005 George South

    2. 2 Topic 3 - Modems The following MCQs are for use in the Modem lab/ tutorial More than one answer may be correct

    3. 3 1. Wav files: Are use to store video files on PCs Are standard files for audio in Windows Are used for polyphonic tunes in mobiles Are a common file format used for UNIX

    4. 4 2.  Typical Sampling Rates used for .wav files are: 10 MHz 44.1 KHz 11.025 KHz 8 kHz

    5. 5 3. Microsoft call files sampled at 22.05 KHz : Radio quality CD quality Telephone quality Speech quality Hint: use the sampling theorem to get the max frequency

    6. 6 4. The speech band on the telephone system is normally quoted as:   100 to 4000Hz 300 to 4000 Hz 0 to 8000 Hz 300 to 3400 Hz

    7. 7 5. The resolution typically used for speech is: 8-bits 16-bit 64-bit 32-bit

    8. 8 6. The last part of the telephone system is : called the local loop analogue digital usually optical fibre

    9. 9 7. A .wav file is sampled at 8 kHz with 8-bit resolution. The data rate required to reproduce it is: 8 kbps 64 kBytes/sec 64 kbps 8 kBytes/sec kbps = kilo bits per second

    10. 10 8. Digital signals cannot be used directly on a telephone system because: It is against the law The speech band has insufficient bandwidth Digital signals involve DC voltages The system was designed for speech not data

    11. 11 9. A 1 kHz square wave has harmonic components at : 1 kHz 2kHz 3kHz 4 kHz etc 1 kHz 3kHz 5 kHz etc 0.5 kHz 1 kHz 2kHz 3kHz 4 kHz etc 1 kHz 10 kHz 100 kHz etc

    12. 12 10. Modem is short for: Modern Demon Modular demodulator Modern Emulator Modulator-demodulator

    13. 13 11. A voice modem : Digitises voice Allows either ordinary telephone activity or data activity Cannot be used for data Cannot use data compression

    14. 14 12. MP3: uses perceptual audio coding and psychoacoustic compression Shrinks sound data by a factor of 10 Uses a codec Was devised by the Moving Picture Experts Group

    15. 15 13. MP3 files: Are still digital and require a modem Cannot be read by Windows utilities Contain tags relating to the content Can contain viruses

    16. 16 14. Unicode: Is a way of representing characters by numbers Uses 8-bits to represent characters Can only handle European languages Uses 16-bits per character

    17. 17 15. ASCII: Was invented by IBM Uses 7 or 8 bits to represent characters Is never used on the Internet Is a subset of Unicode

    18. 18 16. 8-bit ASCII characters are sent over a network: Only the 8-bits need to be transmitted Start and Stop bits are needed Only Start bits are needed The transmission cannot be inactive

    19. 19 17. ADSL is installed on your phone line: The original telephone handset must be replaced by a digital one The bandwidth of your telephone line is much larger Digital signals can be sent without modulation The telephone bandwidth is increased for clearer calls

    20. 20 18. ADSL: Has no requirement for a modem Requires a clever modem which now works with many effective audio bands Has equal upload and download speeds Uses Frequency Modulation

    21. 21 19. Video Conferencing: Has no requirement for data compression Uses the same codec for audio and video Requires audio and video codecs Requires both ends of the conference to have the same codecs

    22. 22 20. Cable systems : Don’t need a modem Can’t work at data rates above 1 Mbps Use similar modulation techniques to ADSL Are fundamentally analog

    23. End of Questions Any errors please report to George South g.south@mmu.ac.uk

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