4.2.3. Analyzer Settings

Analyzer Settings

Figure 4.32. Analyzer Settings

The Analyzer Settings determine the frequency and time resolution and other aspects of the spectrum, spectrogram, and pitch analysis. In particular, the Time Resolution has a large influence on the kind of information that the analyzer will extract from a recording.

Sampling Rate

The Sampling Rate determines the number of measurements (samples) per second recorded from the input source. You can measure frequencies of up to half the sampling rate. For example, if the sampling rate is 11025 samples per second, then the analyzer can measure frequencies up to around 5500Hz. Standard music CDs have a sampling rate of 44100Hz. This should be a reasonable setting for most practical purposes, as it gives a good balance between frequency resolution and sound quality (however, see the note below).

The sampling rate can only be changed on new files, before you have made any recording. The format of existing recordings cannot be changed. If you want to change this setting and it is disabled, click on FileNew first.

VoceVista Video uses two separate mathematical methods to analyze sound. One method is the Fast Fourier Transform (FFT), which calculates the Spectrum. This gives the intensity of the individual frequency components of a sound. The other method is the detection of the fundamental pitch, which is completely separate from the FFT. The two methods are both dependent on the sampling rate of a recording. However, while lowering the sampling rate can increase the accuracy of the FFT in same circumstances, the pitch detection works best with sampling rates of 44100Hz or higher.

Frequency Resolution (FFT Size)

The frequency resolution is the smallest difference between two frequencies that the analyzer can distinguish. Internally, this setting is stored as the size of the Fast Fourier Transform (FFT), which is the number of points that are computed for each update.

A higher FFT Size gives you more accuracy and shows more detail in the spectrum and spectrogram, but it also requires more processing power and may slow down your computer. In general, you should choose the highest setting that still gives you acceptable performance when moving the range slider on the Timeline.

Time Resolution (updates per second)

This setting determines whether the Analyzer should be more accurate in the frequency or in the time domain. In other words, are you more interested in measuring the exact pitch, or in measuring the melody (the variations of the pitch over time)? Fewer updates per second will increase the accuracy of the pitch display but hide the melody, while more updates per second will cause the analyzer to show the melody more clearly, but with less accuracy in the pitch.

Time Resolution for Pitch Detection

This is similar to the Time Resolution for the FFT, but is used by the algorithm for pitch detection, which is separate. The Time Resolution value determines the length of a recording segment that the pitch algorithm considers to find its fundamental pitch. Changing this value is for advanced users only, as the default value works best in most situations.

Sampling Rate and Frequency Resolution

Higher sampling rates are not automatically better, because a higher sampling rate means lower frequency resolution for the same FFT size. To understand what that means, open the Analyzer Settings dialog and experiment with changing the sampling rate from 11025Hz to 96000Hz. Notice how the frequency resolution decreases as the sampling rate increases.

If the sampling rate is doubled, the FFT Size also needs to be doubled to get the same frequency resolution. Therefore, set the sampling rate as high as necessary for the highest frequency that you want to measure, but not higher. If you want to measure very low frequencies (100Hz or lower), lowering the sampling rate will increase the accuracy of the measurement without requiring a larger FFT Size.

The table below shows the spectrum of a tuning fork that is tuned to 105Hz at various FFT Sizes to compare the analyzer accuracy at sampling rates of 11025Hz and of 44100Hz.

Sampling Rate: 11025Hz Sampling Rate: 44100Hz
FFT Size: 2048 Points

Resolution: 5.4Hz

Resolution: 21.5Hz

FFT Size: 4096 Points

Resolution: 2.7Hz

Resolution: 10.8Hz

FFT Size: 8192 Points

Resolution: 1.3Hz

Resolution: 5.4Hz

FFT Size: 16384 Points

Resolution: 0.7Hz

Resolution: 2.7Hz

Table 4.5. Sampling Rate and Frequency Resolution

In this example, the frequency scale range is 75Hz to 135Hz, and the dynamic range is 66dB, starting at -8dB. The time resolution was set to 1 update per second.