Starts a Linearity and Distortion measurement.
Enters the Linearity and Distortion settings dialog box.
Compute Linearity, and is enabled only if Linearity analysis is selected (in the settings dialog, see below). Basically the process consists in dividing the measured output by the supplied input. Doing this greatly simplify realising both DUT gain and deviation from linearity. The following example should clarify things further.
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The graphs refers to a linearity measurement of a Push Pull tube amp. After processing, the Y scale can be expanded, still including the whole span, greatly enhancing detail inspection.
14.2.1 TOOLBAR DROP DOWN LIST
Input channel
Selects the input channel configuration
14.2.2 LINEARITY&DISTORTION SETTINGS DIALOG
X Axis Values
Allows setting the X axis extreme left and right values. Has immediate effect, once OK is pressed, and has only graphical implication; that is it does not affect the actual or next measure span.
X Axis Unit
Can be either Volts or Watts. Has immediate effect and the curve is recalculated accordingly. Changing the impedance in the sweep settings does not affect results as the impedance set at measuring time is taken for calculation. When Vs. input is selected in the X Axis Vs., Volts is forced and the choice disabled.
X Axis Vs.
Selects if the X axis represents DUT output or input values. Input Values can only be expressed in Volts.
Y Axis Scale
Selects how the Y axis is displayed. When anything but Linearity is selected in the
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a bi-logarithmic graph. Selecting dB will plot distortion in dB below fundamental/s. When Linearity is selected dBV or Volts will be used as Y Unit. If the compute linearity button is pressed dB or V/V are used.
Sweep Settings
These are all settings affecting the next measure to be performed. Must be therefore handled with care.
Start and Stop
set the voltage sweep range supplied to the DUT input. Start should be lower in value than Stop. While these values can be chosen in an iterative way, having a rough idea of the DUT gain is a good practice. Notice however that keeping the DistLim parameter to or lower than 10% would prevent hard overload of the DUT. Sweep range stops anyway when the maximum allowed distortion is reached, whatever
Stop value is chosen. Stop value cannot be grater than 3V, being this the CLIO’s
limit.
Step
set sweep resolution in logarithmic equal step.
DistLim
set, in percentage, the maximum allowed distortion before the sweep stop anyway.
Imp,
in Ohm, set the impedance used by the system to calculate power. Should obviously be set to the real impedance that loads the DUT. Changing this value after the measurement has no effect on an already done measure; the value should be correct
before the measure is taken. Att
set the value of an eventually used passive attenuator placed on CLIO’s input. CLIO’s input accept up to 100VRMS, that is 1250W/8Ohm. Should you need more, use a resistors divider on the input and set the Att value accordingly. Advised value are 90-10 Ohm to divide by 10.
Analysis
Through this radio button control the analysis type is selected.
Linearity
measure the output Voltage Vs input Voltage. Output level is measured through FFT looking only at the amplitude of the generated tone. That is harmonics noise or other is not considered in the output level.
THD
measures Total Harmonic Distortion. Again distortion level is calculated via FFT and therefore noise is not taken in account. These, in some limited cases, at lower level, yields to slightly different results than those obtained via traditional THD+noise measurements. This approach is, however, more accurate. For setting the measurement frequency please see below.
SMPTE
measures Intermodulation distortion using SMPTE standard. Two tones are generated
in a 4:1 ratio at 60Hz and 7000Hz. Intermodulation components up to the 5th order
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DIN
measures Intermodulation distortion using DIN standard. Two tones are generated
in a 4:1 ratio at 250Hz and 8000Hz. Intermodulation components up to the 5th order
are considered for distortion.
CCIF
measures Intermodulation distortion using two equal level near spaced (1kHz) in
Frequency tones. Difference Intermodulation components up to the 2th order are
considered for distortion. To keep results directly comparable with THD analysis both output Voltage or Power are single tone equivalent scaled. Considering a power amplifier clipping point, this usually due to the peak value of the signal rather then it RMS value. With two tone of equal level the RMS values is 3dB lower than the same peak to peak single tone.
Freq
Has no effect in SMPTE and DIN analyses which use fixed frequencies. Set the measurement frequency for Linearity and THD. Set the center Frequency for CCIF; for example 15500Hz means two tone are generated, spaced by 1kHz, at 15000Hz and 16000Hz
Chapter 15 - Acoustical Parameters 175
15 ACOUSTICAL PARAMETERS
15.1 INTRODUCTION
With the Acoustical Parameters control panel it is possible to evaluate the acoustical behaviour of a room and carry out sophisticated post processing of a measured impulse response to calculate the acoustical parameters as defined by the ISO 3382 standard. These quantities describe the behaviour of auditoria, concert halls and are applicable to any room intended for speech or music reproduction.