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Technical Report: What is Sound Quality Evaluation 4

10. Example of Analysis

Here, as interesting examples, we will discuss "the sound of a drilling machine and a symphony" and "the sounds before and after warming up a car engine."

10-1 Excavator Sound and Symphony Sound

In the following analysis example, we will compare the sound of a drilling machine with a symphony (Beethoven's 5th Symphony, 4th movement). Although these two sounds are completely different, when conducting a 1/3 octave analysis, which is currently commonly used for sound evaluation, they result in nearly identical spectra as shown in the data below.

There are various parameters for evaluating sound quality, but here we will use roughness, a parameter that represents the coarseness of sound, to compare and evaluate these two sounds. The following graph represents the spectrum of roughness. A higher value indicates a greater 'roughness' of sound, allowing us to clearly capture the difference in 'roughness' between the sound of a symphony and that of a drilling machine.

  • symphony sound
  • img-soundquality-04-03
    excavator sound

Sound before and after warming up a car engine.

Next, I will introduce an example of sound quality evaluation regarding automobile engine noise. The sound quality of an automobile engine differs when the engine temperature is low compared to when it is high. Before warming up, the sound is high-pitched and noticeable, while after warming up, it diminishes. Analyzing these sounds using the conventional 1/3 octave spectrum reveals that the spectrum is almost the same before and after warming up, indicating that traditional methods cannot analyze or evaluate the differences in sound quality before and after warming up.

  • Before warming up operation
  • after warm-up operation

First, we will conduct an analysis using loudness, which is the most fundamental measure of sound quality and can represent values proportional to the volume of sound heard by humans.

The horizontal axis represents frequency, and the vertical axis represents loudness. There is no significant difference in loudness before and after warm-up, and it can be said that the sound levels are almost the same.

  • Before warming up operation
  • after warm-up operation

The following data is the result of an analysis using variability intensity, one of the audio quality evaluation metrics. The horizontal axis represents frequency, and the vertical axis indicates the strength of the variability intensity.

  • Before warming up operation
  • after warm-up operation

Variability intensity is an evaluation measure that expresses the fluctuations in sound volume in a way that humans perceive. A significant difference is observed in the area circled by the red circle on the graph, particularly around the frequency of 4 kHz. These results indicate that the high-pitched, unpleasant variability of the engine noise before warm-up is due to fluctuations in the 4 kHz component. Thus, by using sound quality evaluation metrics, effective analysis of unwanted noises can be conducted.

Finally

To create a more comfortable sound environment, a sound evaluation that is closer to human perception is effective. Ono Sokki will assist in creating a comfortable sound environment.

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