24 db 30 db f 200 2 khz 20 khz 6 khz 12 khz figure

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Unformatted text preview: 3 ) − 1 + What kind of filter is this? (b) Solutions 6-24 R1 R2 M. J. Roberts - 8/16/04 C4 C1 vx(t) + R5 C3 + vi (t) vo(t) R2 - - Similar to (a). (c) R4 R1 C5 R3 vx(t) + + vi (t) vo(t) C2 - - Similar to (a) 33. When music is recorded on analog magnetic tape and later played back, a high-frequency noise component, called tape “hiss” is added to the music. For purposes of analysis assume that the spectrum of the music is flat at –30 dB across the audio spectrum from 20 Hz to 20 kHz. Also assume that the spectrum of the signal played back on the tape deck has an added component making the playback signal have a Bode diagram as illustrated in Figure E33. -24 dB -30 dB f 200 2 kHz 20 kHz 6 kHz 12 kHz Figure E33 Bode diagram of playback signal The extra high-frequency noise could be attenuated by a lowpass filter but that would also attenuate the high-frequency components of the music, reducing its fidelity. One solution to the problem is to “pre-emphasize” the high-frequency part of the music during the recording process so that when the lowpass filter is applied to the playback the net effect on the music is zero but the “hiss” has been attenuated. Design an active filter which could be used during the recording process to do the pre-emphasis. Solutions 6-25 M. J. Roberts - 8/16/04 The pre-emphasis active filter should have a low-frequency gain of one and a highfrequency gain of 6 dB and should transition between those gains between 6 and 12 kHz with a slope (asymptotic slope) of 6 dB/octave. So the pre-emphasis filter should have one real zero to create the first corner and one real pole to create the second corner. If we use the inverting amplifier configuration with an op-amp and make the feedback impedance a resistor then the source impedance can create the zero and pole at the required locations. The design idea is to make the source impedance have the required low-frequency value and then to make its high-frequency value lower, increasing the overall gain at high frequencies,...
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This note was uploaded on 06/19/2013 for the course ENSC 380 taught by Professor Atousa during the Spring '09 term at Simon Fraser.

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