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# Octave Analysis

Due to its logarithmic frequency axis, octave analysis is an indispensable tool for sound measurement as well as predictive monitoring. Dewesoft octave analysis solution meets all of the IEC and ANSI Class I specifications for octave filters.

IEPE
Voltage
FlexRay
Video
Sound
Sound pressure

## Main Features

• TRUE OCTAVE ANALYSIS: true octave filters exactly represents the filter sets defined by the IEC 61260 standards and give the user real-time response for vivid live visualization of data, crucial for advanced acoustic analysis
• SYNTHESIZED ANALYSIS: for large channel count systems Dewesoft provides extremely fast calculation from frequency domain
• RESOLUTION UP TO 1/24 OCTAVE: for deep analysis of data Dewesoft provides very narrow band analysis up to 1/24th octave
• FREQUENCY SOUND WEIGHTING: standard frequency weighting curves (A, B, C, D and Z) can be applied directly in a frequency domain for analysis of sound
• FREQUENCY AVERAGING: block history with linear, peak, exponential averaging or overall calculation is available

## Constant Percentage Bandwidth (CPB)

CPB filter is a filter whose bandwidth is a fixed percentage of a centre frequency. The width of the individual filters is defined relatively to their position in the range of interest. The higher the centre frequency of the filter, the wider the bandwidth.

The widest octave filter used has a bandwidth of 1 octave. Many subdivisions into smaller bandwidths are often used. The filters are often labeled as “Constant Percentage Bandwidth” filters. A 1/1-octave filter has a bandwidth of close to 70% of its centre frequency. The most popular filters are perhaps those with 1/3-octave bandwidths. One advantage is that this bandwidth at frequencies above 500 Hz corresponds well to the frequency selectivity of the human auditory system. DEWESoft supports up to 1/24-octave bandwidth.

## Calculation Principle

### True octave(ANSI, IEC)

Uses filter sets as in analog octave analyzers. One of the main advantages is that we can really see the dynamic behavior of the input data.

### Synthesized

Calculated using FFT as the base and is updated when every FFT is being calculated.

## Frequency Weighting

Frequency weighted noise measurements offer standard ways to measure sound, and we use each of these frequency weightings for different types of measurements.

• A-weighting is applied to measured sound levels in an effort to account for the relative loudness perceived by the human ear. The human ear is less sensitive to low and high audio frequencies.
• B-weighting is the best weighting to use for music listening purposes.
• C-weighting is used for high-level noise measurements.
• D-weighting was specifically designed for use when measuring high-level aircraft noise in accordance with the IEC 537 measurement standard. The large peak in the D-weighting curve reflects the fact that humans hear random noise differently from pure tones, an effect that is particularly pronounced around 6 kHz.
• Z-weighting is linear at all frequencies and it has the same effect on all measured values.

## Averaging Type

Averaging is used to get more stable results. There are three averaging modes available:

• Linear averaging - each FFT counts the same
• Exponential averaging - FFT’s become less and less important with time
• Peak hold averaging - only maximum results are stored and shown

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