Emphasis in Radio Broadcasting | Introduction and Application

In FM broadcasting, sound quality is important. People are always striving to develop new technology to reduce the noise signals in transmission to improve the audio signals and the listening experience. Two of the technologies are Pre-emphasis and De-emphasis. Do you understand them? This share will introduce the definition and the application of Pre-emphasis and De-emphasis to you.


What is Emphasis?

Actually, Pre-emphasis and De-emphasis can be called emphasis together. But why it is divided into Pre-emphasis and De-emphasis? To answer this question, we need to have a basic understanding of Pre-emphasis and De-emphasis.


The Definition of Pre-emphasis

Pre-emphasis is the concept used in transmitting equipment like FM transmitters. It means that prior to some process, such as the current signals being transmitted over cable, a specific range of input frequency will be boosted or the amplitude will be enlarged. In simple words, the sound volume in a specific range is raised.


The Definition of De-emphasis

On the contrary, De-emphasis is the concept used in receiving equipment like FM radios. It means that before the audio signals are transformed into sound and played, the same range of frequency will apply the transformation opposite to the Pre-emphasis. That's means, the sound volume in the specific range will be decreased.


The Differences of Pre-emphasis and De-emphasis

In conclusion, Pre-emphasis and De-emphasis are similar to each other, but they are applied in different equipment and work reversely. But they work for the same purpose - to improve the audio signals.


How Does Emphasis Work?

Pre-emphasis and De-emphasis work together to improve the audio signals. But how do they achieve this purpose?


The Noise in Audio Signals

The signals in relatively higher frequency have a higher signal resistance capability, but it has a worse noise interference capability because the signals in relatively higher frequency have smaller energy than those in relatively lower frequency. So in radio broadcasting, removing the affection of the noise in the higher frequency is important. And Pre-emphasis and De-emphasis solved the problem by improving the SNR of the signals.


Noise Elimination

Let's see how Pre-emphasis and De-emphasis work together to improve the SNR of the signals.


Determine the Frequency

Pre-emphasis amplifies the high-frequency components through a simple Pre-emphasis circuit. Here's a question, how to determine which range of frequency should be amplified? You will see there is a time interval before the signals are amplified. We call the time interval the time constant. It is calculated via the formula T=RC, where R stands for resistance in the circuit and the C stands for the power supply in the circuit. Typically, 25μs, 50μs, and 75μs these three time constants are available, and different countries adopt different time constants as standard. For example, in North America and South Korea, 75μs is used, and in Europe, 50μs is used.


Amplify the Frequencies

If the 75μs is used as the time constant, the pre-emphasis circuit will linearly enhance the frequencies higher than 2123Hz at the rate of 6dB/octave. After enhancing the frequencies, the SNR would be improved because the amplified part of frequencies will offset the noise in the signals. If you can't understand what does dB mean, the share named How To Distinguish DB, DBI, And DBM ? is recommended, and you will have a brief understanding of dB, dBi and dBm.


Return the Frequencies

In order to have a normal frequency response, a De-emphasis circuit should be added to the radio receiver. Just as the same as Pre-emphasis circuit, it has a time interval after receiving the radio waves, and it is the same as the one of Pre-emphasis circuit. For example, 75μs is used in the De-emphasis, then it will attenuate the frequencies higher than 2123Hz at the rate of 6dB/octave.


The Applications of Emphasis in Radio Broadcasting

In radio broadcasting, Pre-emphasis and De-emphasis are adopted in many applications, like FM broadcasting and vinyl (LP record) as they can improve the SNR in the signals effectively. In addition to the transmission of the analog signal, the digital transmission adopts Emphasis as well. Similar to analog transmission, digital transmission used Emphasis for correcting the distortion in transmitting signals at high data rates.





Speaking of which, we know that Emphasis is such a practical technology in radio broadcasting, it effectively improves the radio signals in transmission. If you need to buy FM radio transmitters with Pre-emphasis, please feel free to contact FMUSER. FMUSER is a professional radio broadcasting equipment supplier, you can buy high-quality FM transmitters at satisfying prices.








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