It’s a well-known fact that analog signals need to be treated before they can be transmitted over a communication channel. To be more exact, the higher frequencies in an analog signal need to be amplified before they’re transmitted. The process of getting an analog signal ready for noise-less transmission is called pre-emphasis.
To help our readers better understand the importance of pre-emphasis, we’ve created a small guide that explains all they need to know about the process. Today, we’ll be looking why digital pre-emphasis is needed, how it simplifies signal transmission, and how to remove its effects on an analog signal.
Why Do We Need Digital Pre-Emphasis:
To understand the need of digital pre-emphasis, we must first understand some basic concept pertaining to signal propagation and data transmission. The first fundamental concept that we must acquaint ourselves with is the Nyquist Criteria, which significantly removes the chances of aliasing and noise interference. This theorem states that,
“The sampling frequency must be greater than or equal to twice the maximum frequency element in a signal.”
Mathematically,
fs ≥ 2 fm
Where, fs = Sampling Frequency and fm = Maximum Frequency Component
As the maximum frequency component is always the most susceptible to the effects of channel noise and distortion, we must take special care to avoid aliasing. This is where pre-emphasis comes into the picture. By giving the higher frequency component a substantial gain (increasing its magnitude), we can significantly enhance the signal to noise ratio and increase the quality of the signal!
How is Pre-Emphasis Achieved?
Pre-Emphasis can be accomplished via the help of a simple pre-emphasis network or circuit. This circuit (which is essentially just a well-calibrated filter, as shown below) increases the magnitude of the higher frequency component, making them less susceptible to noise interference.
The technique of pre-emphasis is so helpful that it finds applications in numerous industries. From telecommunications and record cutting to digital audio recording and FM broadcasting transmissions, all industries that deal with the propagation of analog signals rely heavily on pre-emphasis networks.
The Problem With Pre-Emphasis:
Although Pre-Emphasis is a blessing that simplifies the transmission of analog signals, it’s not without its problems. For example, if you were to subject an audio signal to pre-emphasis and hear at the receiving terminal, it would sound completely different.
Generally speaking, it is observed that the subtle elements of the audio signal sound much heavier than before which can be distracting and annoying. Unsurprisingly, the gain given to high frequency components (via pre-emphasis) is to blame for this difference.
Fortunately, the original signal can be recreated at the receiving terminal via the useful technique of de-emphasis. As its name suggests, de-emphasis is the exact antithesis of pre-emphasis and can be understood as the process of removing the magnitude gain we gave to high frequency components in the signal.
By compensating for the gain we added to these components, we can accurately recreate the original signal at the output terminal. While that may seem counter-productive to you at first, the importance of pre-emphasis and de-emphasis can be understood by the fact that it’s much easier to recreate the original signal at the receiving end via these techniques than it’s to remove the effects of noise once it has adversely affected an analog signal!
And that’s why digital pre-emphasis and de-emphasis are so important in today’s day and age. The products that you see on our online store make use of these (and countless other) techniques to reconstruct a signal at the output end. This, in turn, ensures that your circuit is never prone to errors and performs as expected.
We at ADSANTEC house an ever-increasing library of electrical solutions ranging from high-speed analog to digital convertors to active power dividers, delay line, etc. Browse through our online store today to bring your proposed electrical designs to life!