Frequency Submenu:

• Sync
• Phase Degrees
• Freq Hz
• Freq Step Mode
• Reset on Burst
• Reset on Sweep

Sync:

This Sync control is only relevant in Dynamic RTime mode; in other modes it is not shown. Also, it only has an effect when the trigger Source is set to Stim. It has no effect in Intern mode.

When no modulators are active, the sync defaults to the main wave frequency and the sync point is the positive zero-crossing of the waveform. This main wave sync can also be toggled explicitly via this Sync control in the main Freq submenu.

For modulator menus, the Sync control is not shown unless the modulator itself is active. It is also not shown when the modulator Source is set for Page Modulation. When Sync is set on a modulator, the sync point is the positive zero-crossing of the modulator sine wave.

If you set main Freq Sync while in Burst mode, however, the start of the burst will be ignored and sync will be to the next available cycle start, regardless of where it falls in a burst. You will probably only find this useful in special cases.

For Noise Wave sources there is normally no particular sync interval on which to trigger, since there is no repeating pattern in the noise source. Instead, the the sync period is controlled by the Step factor in the Timing menu. This is the case regardless of whether the current Timing mode set to Spec, Slow, or Step. (In modes other than Dynamic RTime, the Noise sync interval is controlled by Burst length, or by some other page with Freq set via StepN.)

This allows you to see the start of each step in Step mode, but it has another use as well: You can slow the trace update rate by an arbitrary amount. Otherwise, the trace would be free-running (just as if you toggled the main Trig off), and wave data would pass by in a blur.

Only a single Sync source may be active at one time. When you toggle Sync on a particular source, whatever other Sync source might have been set is toggled off. The control only toggles 'on' to select a sync source... there is no toggle 'off' except to toggle another Sync 'on'. You may select Sync from any source, either a modulator or main Freq wave, in any component page of either DAC, or from a DigOut setup page.

This control is distinct from the Page Sync selected in the Sync menu. That control selects one of the two PAIR pages or one of the four EACH pages depending upon how Page Mode is set. It is used primarily in Sequential modes or Static RTime.

Phase Degrees - Main Component Wave:

In Burst mode, this is the phase at the beginning of the entire Burst interval, including any Start delay. In other words, Start does not delay the start of the main wave, it just delays the beginning of the burst.

This control is present in the main Freq submenu, and also in the Modulation menus (except Burst) for convenience. It is not available when the main Wave is one of the Noise types.

Freq Hz - Main Component Wave:

Frequency may be set to any value up to the Nyquist frequency, which is half the actual sample rate. If Factor is active, it multiplies the DAC output sample rate, and also the maximum frequency that is allowed.

This control is present in the main Freq submenu, and also in the Modulation menus (except Burst) for convenience. It is not available when the main Wave is one of the Noise types.

The maximum frequency resolution is limited by the effective sample rate:

                          Sample Rate (Hz)
    Resolution (Hz)  =   ------------------
                           65536 × 8192
 

For a sample rate of 48000 Hz, the resolution is thus 0.000089 Hz. The sample rate used here is the effective rate, which is the main ADC sample rate times the oversampling Factor, if active.

The actual frequency entry process is controlled by the Step Mode below it.

When Play Wave type is active, this Freq control changes to Rate. The Play Rate control allows Rate to be given relative to the absolute rate (Abs), as recorded originally, or relative to the current sample rate (Rel).

Frequency Step Mode:

The mode steps through Direct, StepHz, StepN, Octave, and Music on repeated hits of the ENTER key. The mode set here applies to all other Freq adjustments, including modulator frequencies (but not Noise Band edges), but only affects values during adjustment.

Each mode may use a different step size and mechanism. The step size for each mode is set in the Misc menu, after first setting the desired mode in the duplicate mode control there.

Detailed discussions of each mode are provided in the Misc menu section.

Reset on Burst:

In Static mode, each burst presentation is identical since it always starts at the selected Phase setting. In Dynamic mode, however, the main wave continues to run between bursts, and a burst starts at whatever the current phase may be at that instant.

If you toggle this control on, then in Dynamic mode the main wave will be forced to the Phase setting at the start of each burst, just as in Static mode; every burst will be identical.

Why would you want ever-changing bursts? To uncover certain behaviors of the system under test. A typical example is where the response of the system contains two separate components: One responds to the instantaneous waveform, and the other responds only to the spectrum in a phase-insensitive manner. By varying the starting phase and averaging many responses, the contributions of the waveform portion will be minimized. (Sometimes, an even better way to do this is to alternate between two bursts with opposite polarities.)

Reset on Sweep:

When this control is on, each sweep will start at exactly the same phase. If you set Sweep Sync, a recording of the output will appear frozen on the trace.

When this control is off, each sweep will start at whatever phase the main wave had when the prior sweep ended. With Sweep Sync active, the trace will roll continuously even though the start of the sweep is indeed at the trigger sync point. This might be useful to distinguish between response components that are sensitive or insensitive to phase at a given instantaneous frequency.

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