Metric Halo SpectraFoo - Manual (Page 91)

Signal Generator
91
3. Start Level edit-text box: The level entered into this box is used as the starting level of the sweep. This
level is in units of dBFS and may be positive or negative.
4. Start Phase edit-text box: The phase entered into this box is used as the start phase of the signal. The
phase is in units of degrees and may be positive or negative.
5. End Frequency edit-text box: The frequency entered in this box is the frequency of the end of the sweep.
This frequency can be any positive value (fractional or integer). If the frequency entered is negative, it
will be treated as positive. An entry of “*” means “use the start value”.
6. End Level edit-text box: The level entered into this box is used as the ending level of the sweep. This
level is in units of dBFS and may be positive or negative. An entry of “*” means “use the start value”.
7. Pre-Delay edit-text box: The Pre-Delay time is the period of time that will elapse before the sweep starts.
8. Duration edit-text box: The Duration is the period of time that will elapse between the start and end
of the sweep.
9. Post-Delay edit-text box: The Post-Delay time is the period of time that will elapse after the end of the
sweep before the sweep loops around.
Each sweep in the generator loops after the pre-delay, duration, and post-delay time has elapsed. The param-
eters sweep over the duration only. So, if the pre-delay is 1 second, the post-delay is 1 second and the duration
is 10 seconds, the total loop time is 12 seconds.
The generator has two sweep modes. The sweep mode is a global property of the signal generator (the same
mode is used for all sweeps). You can set the mode for the generator with the sweep mode radio buttons:
Figure 8.3: Sweep mode radio buttons
1. The “Lin” button selects a linear parameter sweep. With a linear sweep the sweepable parameters
(Power and Frequency) change at a uniform rate. As an example, if the start frequency is 100 Hz; the
end frequency is 1100 Hz and the sweep time is 10 seconds, the frequency will increase by 100 Hz
every second.
2. The “Log” button selects a exponential parameter sweep. With an exponential sweep the sweepable
parameters (Power and Frequency) change at an increasing rate. This sort of sweep changes the fre-
quency a uniform number of octaves per second and the level a uniform number of dB per second.
As an example, if the start frequency is 100 Hz; the end frequency is 200 Hz and the sweep time is 2
seconds, the frequency will increase by 1/2 octave every second.
Additive white noise with sweepable level
In addition to the swept sine generators, the signal generator also provides additive white noise. The white-noise
generated by SpectraFoo has a uniform level pdf (probability distribution function) and a uniform frequency
pdf. This means that all sample values are equally likely and all frequencies are equally likely. The parameters
for the white noise generator are:
Figure 8.4: White Noise Parameter Cluster
1. Enable checkbox: Checking this turns on the additive white noise.
2. Start Level edit-text box: The peak level of the white noise at the start of the sweep. This level is in units
of dBFS and may be positive or negative.
3. End Level edit-text box: The level entered into this box is used as the ending level of the sweep. This
level is in units of dBFS and may be positive or negative. An entry of “*” means “use the start value”.
4. Pre-Delay edit-text box: The Pre-Delay time is the period of time that will elapse before the sweep starts.