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10 FM Receiver

The document discusses pre-emphasis and de-emphasis in FM stereo transmission. It explains that pre-emphasis boosts higher audio frequencies between 2-15 kHz at the transmitter. De-emphasis then attenuates those same frequencies by the same amount at the receiver. This balances the frequency response and improves signal-to-noise ratio, which is worse for higher frequencies due to noise. The document also briefly discusses mono and stereo speakers as well as 5.1 speaker systems.

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Mohamed shabana
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60 views9 pages

10 FM Receiver

The document discusses pre-emphasis and de-emphasis in FM stereo transmission. It explains that pre-emphasis boosts higher audio frequencies between 2-15 kHz at the transmitter. De-emphasis then attenuates those same frequencies by the same amount at the receiver. This balances the frequency response and improves signal-to-noise ratio, which is worse for higher frequencies due to noise. The document also briefly discusses mono and stereo speakers as well as 5.1 speaker systems.

Uploaded by

Mohamed shabana
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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• Pre-emphasis and De-emphasis

• FM Stereo:
• Spectrum of Baseband Stereo Signal Dr. Ali Muqaibel
• Transmitter Ver. 4.0
• Receiver

Dr. Ali Muqaiel 1


 Pre-emphasis
◦ Pre-emphasis refers to boosting the relative amplitudes of the modulating voltage for higher audio frequencies
from 2 to approximately 15 𝑘𝐻𝑧.
 De-emphasis
◦ De-emphasis means attenuating those frequencies by the amount by which they are boosted.
Amplitude

Pre-emphasis frequency
Pre-emphasis FM FM De-emphasis response
filter filter
transmitter receiver
𝐻𝑝𝑒 (𝑓) 𝐻𝑑𝑒 (𝑓) 3 dB
𝑚(𝑡) 0 dB Combined frequency
Message -3 dB response
+
Noise Noise
De-emphasis frequency
𝑤(𝑡) response
At the output of FM receiver, noise
impact on high frequency Frequency
components is worse than low
frequency 𝑓 = 2.123 𝑘𝐻𝑧

Dr. Ali Muqaiel 2


Mono Speakers
• They have only one channel of audio as input.
• It is a combination of both Right (R) and Left (L)
Channels.
• Enough for voice normal usage.

Stereo Speakers
• They have dual channel audio input.
• These include the Right (R) Channel as well as the
Left (L) Channel.
• Main purpose is for multimedia.
• Needs two or more microphones to record.

Dr. Ali Muqaiel 3


New technology

5.1 Speaker System

Dr. Ali Muqaiel 4


𝑚 𝑡 = 𝐿 + 𝑅 ′ + 𝐿 − 𝑅 ′ 𝑐𝑜𝑠 2𝜋 38𝑘 𝑡 + 𝛼𝑐𝑜𝑠 2𝜋 19𝑘 𝑡

A small carrier of 19𝑘𝐻𝑧


is used as a pilot carrier.

The pre-emphasized signal


(𝐿 − 𝑅)’ uses a carrier of
38𝑘𝐻𝑧 = 19𝑘𝐻𝑧 × 2

Stereophonic has to be compatible with monophonic reception


(𝑅 + 𝐿). The total bandwidth is still 200 𝑘𝐻𝑧 & ∆𝑓 = 75 𝑘𝐻𝑧

Dr. Ali Muqaiel 5


◦ Monophonic FM consist of the upper branch only (𝐿 + 𝑅 complete signal without
stereo effect)
◦ Why 19 𝑘𝐻𝑧 is used?
 No signal component within 4 𝑘𝐻𝑧
◦ What is the effect of adding a pilot carrier?
 Reduction in SNR by 1𝑑𝐵 (read the book for full explanation).
 If the maximum for 𝑅 and 𝐿 is 𝐴𝑝, then the worst case maximum for 𝑅 + 𝐿 & 𝐿
− 𝑅 is |𝑚(𝑡)|max = 2𝐴𝑝 + 𝛼, where 𝛼 represents the effect of the pilot.
 The amplitude is reduced approximately by 0.9 and hence the power is reduced
by 0.81 which is about 1 𝑑𝐵.

Dr. Ali Muqaiel 6


Virtual Barber Shop Hair Cut - 3D Sound (Amazing!!)
https://www.youtube.com/watch?v=8IXm6SuUigI&list=PLC6DD661D892CB6F5&index=9

Dr. Ali Muqaiel 7


Dr. Ali Muqaiel 8
New technology

 Can we see sound?


 http://people.csail.mit.edu/mrub/VisualMic/

Dr. Ali Muqaiel 9

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