The Signal Generator can produce signals of the following types, output simultaneously on both the left and right channels of the selected soundcard output:
The RMS signal level can be set for any of the signal types with 0.1dB
resolution relative to digital full scale. The arrow buttons on the RMS Level
spinner change the value in steps of 1dB, or any required value can be
typed directly into the level box.
The level meter below the play button shows the signal
rms level in dB below full scale, with the peak level shown as a red line.
Sine waves can be generated with frequencies between 10.0 and 20,000.0Hz. The frequency is controlled by entering a value in the Frequency box, or using the arrow buttons to increment or decrement the value in steps of 0.5Hz for frequencies below 200Hz and steps of 1Hz thereafter. The generated sine wave sequences have an integer number of samples at the selected sample rate, the sequences are made long enough to ensure the frequency is accurate to better than 0.1Hz below 1kHz and better than 1Hz thereafter.
The frequency can also be controlled via the graph cursor by checking
the "Frequency tracks cursor" box. When this box is checked the signal generator
frequency is linked to the position of the graph cursor and will change to
follow the cursor frequency as it is moved - the changes are smooth with no
phase discontinuities.
The RMS level can range from -90dB to -3.0dB (-3.0dB is the maximum RMS level for a sine wave before clipping, at this level the peaks are at 0dB).
The Signal Generator can produce sweeps with configurable start frequency/
level, end frequency/level, duration and linear or logarithmic progression.
Sweep duration can be up to 60 seconds. If the "Loop" box is checked the sweep
will repeat continuously.
The Pause button is enabled when a sweep is running, presssing it pauses
the sweep at its current frequency and level (leaving the output on), pressing
Pause again continues the sweep.
The Measurement Sweep signal is used by the Wizard when measuring system response. It consists of a linear sweep from DC to 10Hz, followed by a logarithmic sweep to the chosen end frequency. The sweep duration is 256K samples (approx 5.5 seconds at a 48kHz sample rate). This signal is selected autmatically to make sweep measurements.
The Pink Noise generator uses white noise filtered through a -10dB/decade
filter generated from a weighted sum of a series of first order filters, as
devised by Paul Kellet circa 1999. Stated accuracy is within 0.05dB above
9.2Hz at 44.1kHz sample rate.
The Full Range option outputs the filtered noise directly, giving the widest bandwidth and the greatest low frequency content. The Speaker Calibration option applies 2nd order (40dB/decade) filters at 500Hz and 2kHz, producing a signal with its energy centred on 1kHz. Subwoofer Calibration applies filters at 30Hz and 80Hz. Both are broadly in line with the THX test signal recommendations. Custom Filtered allows low and/or high cut filter frequencies to be set arbitrarily, subject to a minimum bandwidth of 1 octave.
The Wizard automatically adjusts the signal levels for the various options and filter settings so that the RMS values reflect the setting in RMS Level. Note that as Pink Noise has random variations some clipping of peaks will occur at RMS levels above approximately -10dB.
The square wave generator allows duty cycles between 1% and 99% in 1% steps.
The generator enforces level changes at exact sample
intervals. This avoids jitter in the edges of the signal, but means that the
generated frequency may not exactly match the requested frequency as the low
and high periods must be integer numbers of samples long. The exact frequency
that has been generated is shown at the bottom right corner of the frequency
display when the generator is running.
The Measurement Level is the signal level the Wizard will use when measuring channels. It is chosen to provide sufficient signal level at the audio input for accurate measurement whilst allowing headroom for the effects of room gain at resonances. Generally the measurement level will result in an SPL during measurement that is close to the system calibration level(typically 75dB).
The Wave Volume and Output Volume are set by the Wizard as part of
Setting The Measurement Level.
The process is started by pressing the
button.
These controls should not require manual adjustment. See the Notes on Soundcard Volume Controls for further information.
Setting the audio output is described in Getting Started.