Class OscillationParameters

Parameters needed from a config file to detect oscillation components.

Oscillation Event detection

The algorithm to find oscillation events uses a discrete cosine transform or DCT. Setting the correct DCT for the target syllable requires additional parameters. Here is the Profiles declaration in the config file for the flying fox. It contains two profiles, the first for a vocalization and the second to detect the rhythmic sound of wing beats as a flying fox takes off or comes in to land.

Profiles:
    Territorial: !BlobParameters
        ComponentName: TerritorialScreech
        MinHertz: 800          
        MaxHertz: 8000
        MinDuration: 0.15
        MaxDuration: 0.8
        DecibelThresholds:
            - 9.0
    Wingbeats: !OscillationParameters
        ComponentName: Wingbeats
        # The search band
        MinHertz: 200          
        MaxHertz: 2000
        # Min & max duration for sequence of wingbeats.
        MinDuration: 1.0
        MaxDuration: 10.0        
        DecibelThresholds:
            - 6.0
        # Wingbeat bounds - oscillations per second       
        MinOscillationFrequency: 4        
        MaxOscillationFrequency: 6    
        # DCT duration in seconds 
        DctDuration: 0.5
        # minimum acceptable value of a DCT coefficient
        DctThreshold: 0.5
        
        # Event threshold - use this to determine FP/FN trade-off.
        EventThreshold: 0.5
Note

The first parameters are common to all events—see CommonParameters. These parameters determine the search band, the allowable event duration and the decibel threshold.

The remaining parameters are unique to the oscillation algorithm and determine the search for oscillations.

MinOscilFreq and MaxOscilFreq specify the oscillation bounds in beats or oscillations per second. These values were established by measuring a sample of flying fox wingbeats.

The next two parameters, the DCT duration in seconds and the DCT threshold can be tricky to establish but are critical for success. The DCT is computationally expensive but for accuracy it needs to span at least two or three oscillations. In this case a duration of 0.5 seconds is just enough to span at least two oscillations. The output from a DCT operation is an array of coefficients (taking values in [0, 1]). The index into the array is the oscillation rate and the value at that index is the amplitude. The index with largest amplitude indicates the likely oscillation rate, but DctThreshold sets the minimum acceptable amplitude value. Lowering DctThreshold increases the likelihood that random noise will be accepted as a true oscillation; increasing DctThreshold increases the likelihood that a target oscillation is rejected.

The optimum values for DctDuration and DctThreshold interact. It requires some experimentation to find the best values for your target syllable. Experiment with DctDuration first while keeping the DctThreshold value low. Once you have a reliable value for DctDuration, gradually increase the value for DctThreshold until you're no longer detecting target events.

DCT parameters

Figure. Parameters required for using a DCT to detect an oscillation event.
Inheritance
Object
CommonParameters
DctParameters
OscillationParameters
Implements
Inherited Members
Namespace: AnalysisPrograms.Recognizers.Base
Assembly: AudioAnalysisTools.dll
Syntax
[YamlTypeTag(typeof(OscillationParameters), null)]
public class OscillationParameters : DctParameters, IValidatableObject

Implements

Extension Methods