Runco REFLECTION CL-510 Bedienungsanleitung PDF herunterladen (Seite 15)

What’s Your Sign?

Sometimes, newly installed audio wiring is

passed over during the labeling routine and the

polarity from/to the ampliﬁer is unknown. At any

rate, phasing speakers or testing ampliﬁer output

polarity is a common occurrence. The Polarity Test

in the VTG 300 is a unique test signal comprised

of a 1 Hz pulse having a duty cycle of 0.1%

(about 1 millisecond). When connected to the

audio system input, it may be used along with

polarity receivers such as the Galaxy Audio Cricket

or the Rolls PT102 for a rapid veriﬁcation of

cabling connectivity.

Shouldn’t every A/V techie be using video

and audio test signals? Having them in the

palm of your hand certainly enhances the

convenience. With each passing year, the

beneﬁt-to-dollar ratio in electronic systems rises.

The trend includes most measurement tools, like

the venerable oscilloscope. Take it from me:

Learning to use basic, but necessary, audio/video

test signals in an A/V system installation is the

only way you’re going to create those rare

electronic memories for yourself.

TECHNICALLY SPEAKING...

Fall 2003 ExtroNews 14.3 15

most of their needs. The complement includes

white noise, pink noise, sine wave, square wave,

swept sine wave, and a unique polarity test.

Why have “noise” as a test source? White noise

is known as a broadband noise, which means it is

composed of all frequency components at equal

energy level in random order. This characteristic

of wideband noise makes it invaluable when

evaluating the frequency bandpass characteristics

of audio systems. White noise gets its name from

the connotation with white light wherein white

light is said to be composed of an inﬁnite number

of wavelengths of visible energy.

The pink noise source in the VTG is intended as

the standard signal source when evaluating the

acoustic performance of a sound system with a

real-time analyzer. Humans perceive twice the

power level for each octave increase in audible

frequency, so white noise “sounds” as though the

power is rising at 3dB per octave. Pink noise is

lowpass-ﬁltered white noise (at -3dB per octave)

such that, on a real-time analyzer, it appears to

be ﬂat over the entire audible frequency band.

Using Waves

The more common tests in audio systems

evaluate linearity, distortion, gain, etc. The

VTG 300 sine wave source is adjustable in

one-third octave steps from 20 Hz to 20 kHz

with speciﬁc stops at the most commonly used

values, such as 400 Hz and 1000 Hz. A swept

sine wave function may be invoked which

covers the same range, but continuously. A

swept sine wave is useful for evaluating

systems for resonances such as rattles and other

unwanted vibrations. The sweep-time interval is

selectable from 1.5 seconds in seven increments

to 150 seconds.

The square wave is used in amplitude and

phase versus frequency measurements. The

frequency may be set among 25 steps from 20

Hz to 5 kHz. This time-domain test, when viewed

on an oscilloscope, tells the technician about the

quality of rise time, overshoot, ringing, tilt, and

slew rate of the system under test. The ﬁrst four

of these attributes are indicative of the system’s

response in the frequency domain (i.e. low

frequency and high frequency characteristics).

Figure 8: Waveform monitor presentation of

the multiburst pattern.

Figure 7: Vectorscope presentation of

PAL-EBU color bars.

Figure 4: Waveform monitor presentation of

SMPTE color bars.

Figure 5: Vectorscope presentation of

NTSC 75

color bars.

Figure 6: Waveform monitor presentation of

PAL-EBU color bars.

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