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tone generator
The tone generator is useful for running a signal to a device under test (DUT) and measuring the before and after waveforms.  This can be done with the internal tone generator loopback in the Input Devices window.  Or the analog waveform can be split with one output channel looping back to the input and the other output passing through the device under test which then goes into the input.  Baudline is very configurable, and sophisticated test layouts and analysis scenarios are possible. 

The tone generator only runs while in the record mode.  Output from the tone generator is turned off when in either the pause or play modes.

The top part of the tone generator display is the current tone frequency that is being synthesized.  The up and down arrows increment or decrement a particular digit.  This is particularly good for performing stepped sine measurements.  The slider under the frequency display is locked to the upper and lower frequency bounds that are defined in the two frequency boxes directly below it.  The frequency slider can be grabbed and moved and its position represents the current frequency's location relative to the upper and lower frequency bounds.

Note that the mouse wheel can be used to quickly change the frequency in any of the four Hz selection zones.  Just point the mouse at a particular digit and turn the mouse wheel up or down.  The mouse wheel also works with all of the numerous horizontal and vertical sliding widgets.






Function
Above is a picture of the tone generator's Function option menu.  It is a list of the different test signals that baudline can synthesize.  Below are detailed descriptions:
  • sine wave

    A sinusoid is digitally pure and its spectrum consists of a single fundamental with no measurable harmonics.  The sine wave is the default function. 


  • triangle wave

    The triangle wave has a strong fundamental with odd harmonics of decreasing energy. The third harmonic is -17 dB down from the fundamental.


  • square wave

    This is a strong fundamental with odd harmonics of a decreasing energy, but stronger than a triangle wave.  The third harmonic is -10 dB down from the fundamental.  This has a lot of inter harmonic noise which is folded back (aliased) high frequency energy.  The square wave is impossible in the analog realm due to its infinite slope edges.


  • ramp up

    Ramp up is a traditional sawtooth waveform.  It is a strong fundamental with even and odd harmonics of a decreasing amplitude.  The second harmonic is -5 dB down from the fundamental.


  • ramp down

    This is a traditional reverse sawtooth.  It has the same harmonic content as the ramp up since flipping the time direction has no effect on the spectrum.


  • unit impulse

    The unit impulse is like a finite version of the mathematical Dirac delta function which is mostly silence with a periodic positive pulse.  The fundamental and the even, odd, and zeroth (DC) harmonics of all are of equal energy.


  • doublet impulse

    This is like the unit impulse but the single spike is replaced by a positive then a negative spike.  It is a weak fundamental with even and odd harmonics of an increasing energy!  The fundamental is -7 dB down from the second harmonic.  The spectrum looks like it has been run through a high pass filter.


  • pink noise

    Each octave of pink noise has a constant spectral energy.  Pink noise is white noise that is run through a pinking filter (-3 dB/octave slope). 


  • pink 80 Hz LPF

    This is pink noise that has been run through an 80 Hz low pass filter (LPF).  It is an ideal signal for feeding to a subwoofer.


  • white Gaussian noise

    WGN has constant spectral energy at all frequencies with a probability histogram that follows a Gaussian bell shaped curve.  This is truly random noise. 


  • white uniform noise

    This has a constant spectral energy at all frequencies like white Gaussian noise.  The difference is that the probability histogram is uniform (flat).  It has equal probabilities of all amplitudes with the range of amplitudes bounded by the gain value.  Note that because of these equal probabilities, the spectral energy is much higher than it is for white Gaussian noise.  This characteristic makes it a valuable test signal to feed into filters under test, because it has an easier potential to overload them.


  • brown noise

    Brown noise is the random walk, similar to 1/f noise.  The frequency slider controls the delta change of the sample amplitude.  At the zero Hz setting, the change in delta amplitude is zero and it linearly rises the delta amplitude of the full 16 bits at the Nyquist frequency.  Note that the frequency setting has no effect on any of the other noise functions.



Modulation
Create complicated test tones by using modulation to encode information onto a carrier function.  Modulation is a method of regulating the variation of a signal, either in a constant or a manually triggered manner.  Modulation can be thought of as a mathematical operator that manipulates the main function.  See the modulation glossary entry for a complete list and description of modulating types.  Baudline's Tone Generator window supports the following modulation operators:
  • OFF

    No modulation.  This is the default setting.  Having modulation set to OFF just outputs the selected Function at a constant frequency.  The baudline spectrogram and spectrum image to the right depicts a pure 1210 Hz sine wave with no modulating operator.

  • FM

    Frequency Modulation.  Modify the main carrier frequency by a secondary function with respect to time.  This has the effect of moving the main frequency slider in a smooth and phase continuous manner.  See the Modulation Function option menu below for a list and description of FM function types.  The lower and upper frequency boxes control the bottom and top FM limits.  An adjustable fourth frequency box controls the frequency of the secondary modulating function.  The baudline spectrogram image to the right shows a sine wave being modulated by the sine function.

  • AM

    Amplitude Modulation.  Like FM but modify the main carrier amplitude by a secondary function with respect to time.  This has the same effect as moving the digital gain slider in a smooth and continuous manner.  See the Modulation Function option menu below for a list and description of AM function types.  An adjustable fourth frequency box controls the frequency of the secondary modulating function.  The depth slider controls the damping to zero (silence) percentage.  The baudline spectrogram and spectrum to the right illustrates a 1210 Hz pure sine wave that is being amplitude modulated by 400 Hz sine with a 20% depth.  Notice the upper and lower sidebands that are offset from the carrier frequency by 400 Hz.

  • pulse

    Pulses are manually triggered continuous waveform bursts of a programmable duration.  The pulse can either start with positive or negative phase.  The duration can range from half a cycle to up to 10 minutes.  Pressing the Manual Trigger button will start and stop the function pulse.  The spectrogram image to the right displays three manually triggered sine wave pusles.

  • sweep

    Generate a frequency sweep.  Just like with the FM operator, the sweep operator uses the same lower and upper frequency boxes to control the top and bottom of the sweep range.  A linear or an exponential sweep shape can be selected along with an upward or a downward frequency sweep direction.  The sweep duration can range from 50 ms to up to 1 hour.  Pressing the Manual Trigger button will start and stop the function sweep.  The baudline spectrogram on the right demonstrates an exponential upward frequency sweep of a sine wave function. 

    Frequency sweeps are extremely useful as stimulus signals for measuring a systems frequency response.  A linear frequency sweep has a white excitation spectrum, while the exponential frequency sweep has a pink excitation spectrum.  For more information on DUT sweep measurements see the Swept sine vs. WGN application note.




Modulation Function
This is the secondary function that operates on either FM or AM modulations.  The Modulation Function has its own frequency selector box that can be adjusted like the primary frequency box.  Available functions are: sine, triangle, square, forward and reverse sawtooths, and brownian motion.  The default is the sine function.
  • brownian motion

    Brownian motion is like brown noise but in this case the drunkards random walk modulates a frequency instead of moving a sample amplitude.  See the baudline spectrogram on the right for an example of a sine wave source that is being frequency modulated (FM) by the brownian motion function.


Output Device
This is the audio card that is selected for output.  Currently only a single card can be used for tone generation output.



Channel
This can put the tone generator output on the left, right, or both channels which would be the center channel.  This can also make one of the output channels 180° out of phase which will push the panning hard into the surround channel.  Or, if the complex option is chosen, then the tone generator output will be in quadrature.

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