# Inverse dft and dft question

• seamie456
In summary, the conversation discusses how to edit the input sequence and results in order to calculate the inverse DFT using the DFT algorithm. It explains the definition of DFT and inverse DFT, and how to obtain the inverse DFT using the DFT. The conversation also mentions the use of conjugation in the process.

#### seamie456

How does one edit the input sequence and the results so as to be able to calculate the inverse dft with the dft algorthm?

if you define the DFT by:
$$X_k = \sum_{n=0}^{N-1} x_n e^{-i 2 \pi \frac{k}{N} n} = DFT\left(x\right)_k$$
and it inverse DFT by
$$x_n = \frac{1}{N} \sum_{k=0}^{N-1} X_k e^{+i 2 \pi \frac{k}{N} n} = IDFT\left(X\right)_n,$$
then the way to get $x_n$ from $X_k$ using a DFT would be something like,
$$x_n = \frac{1}{N} \left(\sum_{k=0}^{N-1} X_k^* e^{-i 2 \pi \frac{k}{N} n}\right)^* = \frac{1}{N} \left( DFT \left( X^* \right) \right)_n^*$$.
where the asterix represents conjugation. Does that make sense?

jason

## 1. What is the difference between inverse DFT and DFT?

The Discrete Fourier Transform (DFT) is a mathematical operation that converts a signal from its original time domain into the frequency domain. The Inverse Discrete Fourier Transform (IDFT) is the reverse operation, converting a signal from the frequency domain back to the time domain. In other words, the DFT decomposes a signal into its frequency components, while the IDFT reconstructs the original signal from its frequency components.

## 2. How is the DFT used in signal processing?

The DFT is a powerful tool in signal processing because it allows us to analyze the frequency components of a signal. This can be useful in applications such as audio and image processing, where certain frequency components may need to be filtered out or enhanced.

## 3. Can the DFT be calculated without using a computer?

Yes, the DFT can be calculated by hand using mathematical equations and complex numbers. However, for larger and more complex signals, it is more efficient to use a computer to perform the calculations.

## 4. What are some common applications of the IDFT?

The IDFT is commonly used in telecommunications, audio and image compression, and data compression. It is also used in solving differential equations and in signal reconstruction.

## 5. What are some limitations of the DFT?

One limitation of the DFT is that it assumes the signal is periodic, which may not always be the case in real-world applications. It also has a finite resolution, which means it may not be able to accurately represent very high or very low frequency components. Additionally, the DFT can be computationally expensive for larger signals, which can limit its use in real-time applications.