Hilbert Transform: Formula, Signals

The Hilbert transform is a mathematical tool that has found extensive use in signal processing, particularly in the analysis of time-varying signals. Named a...


2/5/20243 min read

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The Hilbert transform is a mathematical tool that has found extensive use in signal processing, particularly in the analysis of time-varying signals. Named after the German mathematician David Hilbert, this transform provides a way to extract the analytic signal from a given real-valued signal. In this article, we will explore the definition, formula, applications, and how to combine the Hilbert transform with other indicators. We will also delve into a brief biography of David Hilbert.

Definition of Hilbert Transform

The Hilbert transform is an integral transform that operates on a real-valued function, transforming it into a complex-valued function. Given a real-valued signal, the Hilbert transform produces an analytic signal, which consists of a complex-valued signal with positive frequency components and their corresponding negative frequency components.

Formula for Hilbert Transform

The Hilbert transform of a real-valued signal x(t) is denoted as H{x(t)} and can be calculated using the following formula:

H{x(t)} = \(\frac{1}{\pi}\)PV \(\int_{-\infty}^{\infty}\) \(\frac{x(\tau)}{t-\tau}\) d\(\tau\)

where PV stands for the Cauchy principal value of the integral.

Signals and Applications

The Hilbert transform finds applications in various fields, including telecommunications, audio processing, image processing, and biomedical signal analysis. It is particularly useful in analyzing time-varying signals and extracting relevant information.

One of the significant applications of the Hilbert transform is in the field of instantaneous frequency analysis. By applying the Hilbert transform to a signal, we can obtain the instantaneous frequency of the signal as a function of time. This information is valuable in various applications, such as speech recognition, radar signal processing, and vibration analysis.

The Hilbert transform is also used in amplitude demodulation, where it separates the envelope of a modulated signal from the carrier frequency. This technique is widely employed in radio communication systems and audio processing.

How to Use the Hilbert Transform

To use the Hilbert transform, follow these steps:

  1. Obtain the real-valued signal that you want to analyze.

  2. Apply the Hilbert transform to the signal using the formula mentioned earlier.

  3. The output of the Hilbert transform will be a complex-valued signal, which represents the analytic signal.

  4. Extract the desired information from the analytic signal, such as instantaneous frequency, amplitude, or phase.

Combining the Hilbert Transform with Other Indicators

The Hilbert transform can be combined with other indicators or techniques to enhance signal analysis and processing. Here are a few examples:

  1. Envelope Detection: By taking the magnitude of the analytic signal obtained from the Hilbert transform, we can extract the envelope of the original signal. This technique is useful in applications such as speech processing, audio effects, and fault detection.

  2. Phase Analysis: The Hilbert transform can be used to extract the phase information from a signal. By combining the phase information with other indicators, we can perform phase analysis, which is valuable in applications like audio source separation, speech recognition, and vibration analysis.

  3. Instantaneous Frequency Estimation: The Hilbert transform provides a straightforward way to estimate the instantaneous frequency of a signal. By combining this information with other indicators, we can perform frequency analysis, which is useful in applications such as music analysis, speech processing, and radar signal analysis.

Biography of David Hilbert

David Hilbert was born on January 23, 1862, in Königsberg, Prussia (now Kaliningrad, Russia). He was a renowned German mathematician who made significant contributions to various branches of mathematics, including algebra, number theory, mathematical physics, and the foundations of mathematics.

Hilbert's work on integral equations and mathematical physics led to the development of the Hilbert transform, which bears his name. Throughout his career, he made substantial contributions to the fields of functional analysis, algebraic number theory, and mathematical logic.

David Hilbert's influence extended beyond his own research. He played a crucial role in shaping the mathematical community of his time and mentored several prominent mathematicians, including Hermann Weyl and John von Neumann. Hilbert's famous lecture in 1900 at the International Congress of Mathematicians in Paris outlined 23 unsolved problems, which became known as Hilbert's problems and had a profound impact on the development of mathematics in the 20th century.

Hilbert's contributions to mathematics and his influence on future generations of mathematicians make him one of the most celebrated mathematicians in history. He passed away on February 14, 1943, leaving behind a rich legacy of mathematical achievements.


The Hilbert transform is a powerful mathematical tool that has found widespread application in signal processing and analysis. By transforming real-valued signals into analytic signals, the Hilbert transform provides valuable information about the instantaneous frequency, amplitude, and phase of a signal. Understanding the definition, formula, and applications of the Hilbert transform, as well as its potential for combining with other indicators, can greatly enhance signal analysis and processing in various fields.

Furthermore, exploring the life and contributions of David Hilbert, the mathematician behind the Hilbert transform, adds historical context and appreciation for the development of mathematical tools that continue to shape our understanding of the world today.

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