VGGish Preprocess

Preprocess audio for VGGish feature extraction

Since R2022a

• 

Libraries:
Audio Toolbox / Deep Learning

Description

The VGGish Preprocess block generates mel spectrograms from an audio input that you can then feed to the VGGish pretrained network or to a network that accepts the same inputs as VGGish.

Examples

Compare VGGish Embeddings Block with Equivalent VGGish Blocks

Show that VGGish Embeddings block is equivalent to the cascade of VGGish Preprocess block and VGGish block.

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Ports

Input

Port_1 — Sound data

column vector

Sound data, specified as a one-channel signal (column vector). If Sample rate of input signal (Hz) is 16e3, there are no restrictions on the input frame length. If Sample rate of input signal (Hz) is different from 16e3, then the input frame length must be a multiple of the decimation factor of the resampling operation that the block performs. If the input frame length does not satisfy this condition, the block throws an error message with information on the decimation factor.

Data Types: single | double

Output

Port_1 — Mel spectrogram

96-by-64 matrix

Mel spectrogram generated from the input audio signal, returned as a 96-by-64 matrix, where:

• 96 –– Represents the number of 25 ms frames in each mel spectrogram

• 64 –– Represents the number of mel bands spanning 125 Hz to 7.5 kHz

The overlap between consecutive 96-by-64 mel spectrograms is determined by the value of the Overlap percentage (%) parameter. You can provide the mel spectrogram as an input to the VGGish pretrained network or to a network that accepts the same inputs as VGGish.

Data Types: single

Parameters

Sample rate of input signal (Hz) — Sample rate of input signal in Hz

16e3 (default) | positive scalar

Sample rate of the input signal in Hz, specified as a positive scalar.

Overlap percentage (%) — Overlap percentage between consecutive mel spectrograms

50 (default) | [0 100)

Specify the overlap percentage between consecutive mel spectrograms as a scalar in the range [0 100).

Block Characteristics

Data Types	double | single
Direct Feedthrough	no
Multidimensional Signals	no
Variable-Size Signals	no
Zero-Crossing Detection	no

Algorithms

Preprocessing Steps

The VGGish Embeddings block preprocesses the audio data using the following steps to be in the format required by the VGGish network.

1. Cast the audio data to single precision and resample to 16 kHz.

2. Compute one-sided short-time Fourier transform using a 25 ms periodic Hann window (400 samples) with a 10 ms hop (160 samples) and a 512-point DFT.

3. Convert the complex spectral values to magnitude and discard phase information.

4. Pass the one-sided magnitude STFTs through a 64-band mel-spaced filter bank. Doing so converts the 257-length STFT vectors to 64-length vectors in the mel scale.

5. Convert the 64-length vectors to a log scale.

6. Buffer the vectors into outputs of size 96-by-64, where 96 is the number of spectra in the mel spectrogram and 64 is the number of mel bands. The overlap between consecutive 96-by-64 mel spectrograms is determined by the value of the Overlap percentage (%) parameter.

References

[1] Gemmeke, Jort F., Daniel P. W. Ellis, Dylan Freedman, Aren Jansen, Wade Lawrence, R. Channing Moore, Manoj Plakal, and Marvin Ritter. “Audio Set: An Ontology and Human-Labeled Dataset for Audio Events.” In 2017 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 776–80. New Orleans, LA: IEEE, 2017. https://doi.org/10.1109/ICASSP.2017.7952261.

[2] Hershey, Shawn, Sourish Chaudhuri, Daniel P. W. Ellis, Jort F. Gemmeke, Aren Jansen, R. Channing Moore, Manoj Plakal, et al. “CNN Architectures for Large-Scale Audio Classification.” In 2017 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 131–35. New Orleans, LA: IEEE, 2017. https://doi.org/10.1109/ICASSP.2017.7952132.

Extended Capabilities

C/C++ Code Generation
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Version History

Introduced in R2022a