Analyzer Settings

In Spectrum or Multiplexer mode, it is possible to adjust the “Banding”. When the banding is turned off, all frequency bins of the spectrum are displayed, allowing for a highly detailed analysis. However, this setting requires more CPU power as the amount of data that needs to be calculated and displayed increases with the FFT size.

Spectrum mode is shown in the example below when Banding is turned off.

On the other hand, when banding is turned “On”, frequency bins are grouped together. The width of each group can be adjusted by fractions of an octave, such as Oct12, which means that one band has the width of a 12th of one octave.

Spectrum mode is shown in the example below when Banding is turned on.

• Time: Displays source channels in the time domain (one block of 4096 samples).
• Spectrum: Displays the spectrum of the source channels.
• Multiplexer: Switches the RTA into a multiplexer mode where multiple source channels are combined to two average channels.
• Phase: Displays the magnitude and phase of the source channels. Phase can be wrapped and unwrapped using Graph Settings in the settings window. The phase measurement is done by a dual channel FFT analysis.
• Delay: Displays source channels in the time domain. The delay measurement is done by cross correlation between a reference channel and a channel which contains the reference signal which went through a certain path (example – amp – speaker – microphone). From the position of the maximum within the correlation result the delay can be calculated. Calculated Delay value is displayed in Channel viewer in Delay column.
• IR: Displays the magnitude and IR of the source channels. This is an Impulse response measurement with exponential sine sweep. When this analyzer mode is selected ‘ExpSweep’ Generator mode is set, and you are not allowed to change to other modes. ‘Play’ button is disabled in Generator view and with ‘Single’ button he can generate ‘ExpSweep’ once.

Depending on the test signal, smoothing of the spectrum over time is required. This can be set by the “Averaging” option.

Following are the averaging options available.

• Fast: Small smoothing time constant and hence only a small amount of smoothing (time constant 125 ms).
• Slow: Large smoothing time constant and hence significant smoothing (time constant 1000 ms).
• Custom: Custom smoothing time constant and a textbox where user can enter custom time constant in ms

You should be able to select time constant for peak trace. Depending on the time constant setting, the peak hold trace shall show the maximum value which occurred within the defined moving time window.

Peak Hold settings include:

• Slow
• Fast
• Forever

The length of the FFT which is used for the spectrum calculation can be set between starting from 4096 up to 131072 samples (4k to 128k). The higher the value, the finer the frequency resolution of the spectrum. But with increasing lengths the CPU load will increase due to the higher number of calculations and data to plot.

You can specify how a finite data set is extracted from the roughly infinite input data stream using the “FFT Window”. The “FFT Length” determines how the data set is cut out.

For more details about windowing, refer to the Window Functions.

“Hann” will be the default value for the FFT window.

The Weighting function allows you to select how the input signal is weighted across the frequency range. This can be customized separately for time domain measurements (Freq Weight RMS) and frequency domain measurements (Freq Weight FFT).

For more details about weighting, refer to the A-weighting.

• Off: Disables the peak hold feature.
• Fast: Sets the hold time to 1 sec.
• Slow: Sets the hold time to 5 sec.
• Forever: Holds the peak values until the Reset button in the ribbon bar is clicked.
  

Averaging RMS: The time constant for the RMS calculation can be selected under “Sound Level Meter”.

• Off: No smoothing
• Fast: Small smoothing time constant and hence only a small amount of smoothing.
• Slow: Large smoothing time constant and hence significant smoothing.
• Forever: Extreme smoothing time constant.

Average Mode: The analyzer mode “Multiplexer”, where multiple channels are added to a single “Average” channel can be set to “Time” and “Freq”.

• Time: In “Time” mode the analyzer works as a multiplexer. It combines multiple input audio signals into one audio signal by dividing the input channels into equal fixed-length time slots and mix them into a common output channel with fading between channels. The length of the time slots and the fading characteristic can be configured during runtime. The output signal is the signal of one input channel at a time. If the last input channel is reached, the next input channel will be the first input channel again. Since in this mode only on or two spectrums are calculated it can be used when CPU load is an issue.
• Freq: In “Frequency” mode the analyzer calculates the spectrum of each individual channel and calculates the average of all spectrums. This method is faster and more precise because there are no artefacts from switching between channels as it would occur in the “Time” mode.

Clipping occurs when the input signal exceeds the full-scale range of the input sound device. RTA can detect this condition and signal it. There is also an option to exclude the data packet which contains clipped data from the analysis.

Clipping Detection mode includes:

• Off: Disables clipping detection.
• On: Enables clipping detection.
• ExcludeData: Enables clipping detection and excludes clipped data packets from being analyzed.

When data are clipped, and the detection is enabled a “DATA CLIPPED” message on the top right corner of the graph is shown.

Activating the multiplexer mode to “Time” allows you to set the length of a time slice (referred as “Period Time”) and the time duration for fading one channel into the next (referred as “Fade Time”).