Inverse FFT (Not in Base Package)

Computes the inverse fast Fourier transform (FFT) or the inverse discrete Fourier transform (DFT) of the input sequence FFT {X}. You can use this polymorphic VI to compute the inverse real FFT or the inverse complex FFT. You must manually select the polymorphic instance to use. Details  

Inverse Real FFT

	FFT {X} is the complex input sequence.
	X is the inverse real FFT of FFT{X}.
	error returns any error or warning from the VI. You can wire error to the Error Cluster From Error Code VI to convert the error code or warning into an error cluster.

Inverse Complex FFT

	FFT {X} is the complex input sequence.
	X is the inverse complex FFT of FFT{X}.
	error returns any error or warning from the VI. You can wire error to the Error Cluster From Error Code VI to convert the error code or warning into an error cluster.

Inverse FFT Details

Inverse Real FFT

The input sequence is complex-valued. The Inverse Real FFT VI automatically determines the options, which are the inverse real FFT of a complex-valued sequence if the size is a power of 2 and the inverse real DFT of a complex-valued sequence if the size is not a power of 2.

The Inverse Real FFT VI executes inverse fast radix-2 FFT routines if the size of the input sequence is a valid power of 2

size = 2^m.

m = 1, 2, …, 23.

If the size of the input sequence is not a power of 2, but is factorable as the product of small prime numbers, the VI uses a mixed radix Cooley-Tukey algorithm to efficiently compute the DFT of the input sequence.

Inverse Complex FFT

You can use the Inverse Complex FFT VI to perform an inverse FFT on an array of one of the complex numeric representations.

If Y represents the output sequence, then

Y = F^–1{X}.

You can use the Inverse Complex FFT VI to perform the following operations when FFT {X} has one of the complex LabVIEW data types:

• The inverse FFT of a complex-valued sequence X
• The inverse DFT of a complex-valued sequence X

The Inverse Complex FFT VI first analyzes the input data and, based on this analysis, inverse Fourier transforms the data by executing one of the preceding options. All of these routines take advantage of the concurrent processing capabilities of the CPU and FPU.

Number of Samples Is a Valid Power of 2

The Inverse Complex FFT VI computes the inverse FFT by applying the fast radix-2 FFT algorithm when the number of samples in the input sequence X is a valid power of 2, as defined by the following equation.

n = 2^m,

for m = 1, 2, 3, …, 23, and where n is the number of samples.

The longest sequence with an inverse complex FFT that the Inverse Complex FFT VI can compute is 2²³ (8,338,608 or 8M).

Number of Samples Is Not a Valid Power of 2

The Inverse Complex FFT VI computes the inverse DFT by applying an efficient DFT algorithm when the number of samples in the input sequence X is not a valid power of 2 or is factorable as the product of small prime numbers.

The longest sequence with an inverse complex DFT that the Inverse Complex FFT VI can compute is 2²² – 1 (4,194,303 or 4M – 1).

Refer to the Fast FFT Sizes section of Chapter 4, Frequency Analysis in the LabVIEW Analysis Concepts manual for more information about fast FFT input sequence sizes.