The STx Recorder is supplied with a level meter. Digital recordings allow no overload at all. For that reason it is extremely important to adjust the signal input level to -12 dB in average, providing enough headroom for signal peaks.
The normal recorder can use all standard windows audio devices. A special recording script for ASIO devices with up to 128 channels is included in the program package.
Real Time Spectrum Analyser
STx provides a 2-channel Real Time Analyser (RTA) to be called either as a stand alone application or additionally in combination with the STx-Recorder. The RTA offers the following functions:
- FFT-Amplitude Spectrum (STFT), Waterfall display and Spectrogram
- Linear Prediction Coding (LPC) - smoothed spectrum, Waterfall display and Spectrogram
- Cepstrum smoothed spectrum , Waterfall display and Spectrogram
- Display amplitude spectrum minus Cepstrum smoothed spectrum (cp & sp.-cp).
- Display amplitude spectrum channel A and channel A-B
- Linear and BARK frequency scaling
- Selection of FFT-frame length (frequency resolution) and overlap (hopsize) over large ranges
- Linear and Exponential Spectrum Averaging
- Waveform display.
- Selection of input device and source channel configuration
- Special graphic prensentation modes (full screen, no frame, etc.)
- Variable color scale and graphics properties
Waterfall Display (Frequency axis in BARK).
FFT Amplitude Spectrum (white) with LPC-smoothed spectrum overlayed (yellow)
Note: the LPC-spectrum represents the all-pole model of unnasalized voiced speech signals. The spectral peaks indicate the resonance frequencies of the vocal tract (formants F1, F2, ...). The order of the model is specified by # of coefficients.
Segmentation and Annotations
STx uses segments to address a part of a sound file.
- annotations for each segment can be set
- templates can be used to define annotation variables and default values
- annotations can be stored with the project (unlinked) or with each sound file (linked)
Tools for Segmentation and Annotation:
Visualization, labeling and annotation of sound data in the time domain, narrow segmentation
(e.g. phonetic transcription, full Unicode support)
Frequency analysis (FFT, DFT, Wavelet, Wigner)
Spectrogram - Visualization in Time-Frequency Plane
- large set of time-frequency transformations: FFT, DFT, Cepstrum, LPC, Wavelet, Wigner
- time synchronous display of spectrogram, waveform and parameters (e.g. fundamental freuquency track, formant tracks, rms)
- labeling and annotation of time-varying signals by means of spectrograms (in the frequency domain)
- sectioner - display spectrum at selected time positions
Wavelet Time-Phase Diagram:
The picture shows the comparison of partial #8 of 4 different music strings.
Narrow Band Spectrogram with formant tracks (overlayed) and f0 track
- Cepstrum Analysis: free selection of order (liftering)
- Linear Prediction Coding (LPC) Analysis: free selection of model order
De-noising, signal enhancement
spectral subtraction, frame averaging, signal expansion
Auditory perception modelling - (Computational Hearing)
Comparison of auditory model with LPC-model (for speech)
Simultaneous Masking - Over-Masking: spectral relevance
To identify gear orders in a multiple motor component environment a specific method for the generation of order spectrograms has been implemented. The method applies smoothing on the rpm-signal and uses re-sampling as well as the Discrete Fourier Transform (DFT) in combination with the anti aliasing filter to create order analysis spectrograms at reasonable computational cost.
The Sequencer is a tool to combine synthetic signals and soundfile segments to a virtual signal stream. Originally it was designed, to create test signals for audio experiments.
For more details see: STx-Sequencer.pdf
The spectrogram shows from left to right the real time filtering of white noise: Lowpass, Highpass, Bandpass and Bandstop