SoundMeter offers an advanced, two-channel signal generator tool, capable of producing an assortment of simple and complex waveforms for test and measurement, as well as for demonstration.
Noise excitation signals include random, Maximum Length Sequence (MLS), or periodic pseudorandom noise with white or pink weighting. The period of the MLS and pseudorandom noise sequences can be selected from the sequence length picker.
The Weighting segmented control selection determines whether white noise or pink noise is generated. True white noise contains equal energy at all frequencies. Pink noise contains equal energy per octave (or fractional-octave) frequency band.
Each noise type can be independently switched on or off, which means the three noise types can be mixed with each other, and/or with other signal types.
Maximum Length Sequence (MLS)
A maximum length sequence is a special binary sequence that exhibits properties that make it useful as a pseudorandom excitation signal. It has a white spectrum and a low crest factor, which allow it to be used in system measurements. An MLS of order N has a length of 2^N-1 (where 2^N means 2 to the Nth power). The signal generator produces MLS signals of order 5 through 20.
Sine sweeps can be generated with a linear or logarithmic sweep rate. The linear sweep exhibits a flat magnitude response within a single FFT (as long as the FFT analyzer is using a uniform data window), and the log sweep exhibits a pink magnitude response (a pink response has a 3dB per octave drop in magnitude with increasing frequency).
The sweep can be turned on or off independent of the other signal types. A linear sweep increases (or decreases) in frequency at a constant rate. A logarithmic sweep is faster at higher frequencies than lower frequencies--its sweep rate increases exponentially with frequency.
Lower Frequency, Upper Frequency
Into these text boxes, the lower and upper frequency limits of the sweep can be entered.
The duration of the sweep can be entered (and shown) in units of seconds or samples (at a sampling rate of 48000 Hz, a duration of 48000 samples corresponds to 1 second). The duration itself is entered in the text box and units are chosen from the segmented control to the right of the text box. When either U/D (Up & Down) or DU (Down & Up) is selected for the Sweep Direction, the duration applies to each sweep direction (up and down), so the total sweep duration is twice the duration shown.
The direction of the frequency sweep can be set to one of four options. Choosing Up will cause the chirp signal to begin at the frequency shown in the Lower Frequency text box and sweep to the frequency shown in the Upper Frequency text box. Choosing Dwn (Down) will cause the frequency to sweep in the opposite direction. Choosing U/D (Up & Down) or D/U (Down & Up) will cause the frequency to be swept twice--first in one direction, then the other.
A periodic waveform generator produces a single sinusoid (tone), square, tringle, or sawtooth shaped waveform.
Independent wavforms can be configured for the A and B selections.
The waveform frequency can be set by direct entry in a text box, or by adjusting the frequency slider. The slider's frequency range can be adjusted by entering lower and upper limits in the two text boxes labeled Slider Range. Available signal frequencies are limited to less than half of the sampling rate (the Nyquist frequency).
When Rectangle is selected, a text box appears in which a duty cycle can be chosen for the rectangular wave. The duty cycle refers to the percentage of one period of the waveform in which the signal is high (greater than 0, or greater than the mean).
The controls for the Waveform B selection are identical to those for Waveform A, with the exception of the Relative Phase text box.
When both A and B waveforms are switched on, the phase relationship between the two signals is determined by the value in the Relative Phase text box (given in units of degrees). Waveform B lags behind Waveform A by the chosen Relative Phase.
The amplitude or pan of each signal type can be adjusted. Amplitude and pan settings are stored individually for each signal type.