Log Power FFT

Create a log₁₀(|fft|²) stream chain, with real or complex input.

Parameters

(R): Run-time adjustable

FFT Size

Number of FFT bins

Reference Scale

Sets 0 dB value input amplitude

Frame Rate

Output frame rate

Average (R)

Whether to average [True, False]

Average Alpha (R)

FFT averaging (over time) constant [0.0-1.0]

Example Flowgraph

This flowgraph can be downloaded from Media:Log Power FFT.grc.

Flowgraph Description: Log Power FFT Spectrum Analysis

This flowgraph, created in GNU Radio Companion (GRC), showcases the Log Power FFT block's ability to compute and display the logarithmic power spectrum of a 1 kHz sine wave. Below is a concise overview of its components, configuration, and output:

- Signal Source: Generates a 1 kHz sine wave with an amplitude of 1, sampled at 32 kHz (32,000 samples per second). This provides a single-tone input for analysis. - Throttle: Set to 32 kHz to regulate the data flow, ensuring real-time visualization without overwhelming the system. - Log Power FFT: Processes the input signal to produce a logarithmic power spectrum. Key parameters include:

 - FFT Size: 1024, creating 1024 frequency bins with a resolution of 31.25 Hz (32,000 Hz / 1024).
 - Reference Scale: 512, setting the sine wave's peak at 0 dB in the output.
 - FFT Shift: Enabled, centering the spectrum with 0 Hz in the middle.

- QT GUI Vector Sink: Visualizes the spectrum, spanning -16,000 Hz to +16,000 Hz on the x-axis. The output displays a prominent peak at ±1,000 Hz at 0 dB, reflecting the input sine wave, with a noise floor between -200 dB and -150 dB.

This flowgraph effectively illustrates how the Log Power FFT block converts a time-domain signal into a frequency-domain representation, offering a clear view of the signal’s spectral characteristics.

Source Files

Python Source

Here

Block definition

Here