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发表于 2019-12-17 09:55:42
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J-test is an AES3 test signal that was developed to
maximize the coherence of data patterns while at the same
time providing a basic high-level stimulus tone. This test
stimulates worst-case levels of data-jitter. The signal has two
components, the first being an un-dithered square wave
with a period of 4 samples. A cycle of this is shown here in
hexadecimal notation:
C00000 (-0.5)
C00000 (-0.5)
400000 (+0.5)
400000 (+0.5)
On conversion to analog at a sample rate of 48 kHz this
signal would produce a sine wave with an amplitude of
–3.01 dB FS at 12 kHz. (It looks like a square wave with a
peak amplitude of –6.01 dB FS but in a properly
band-limited system this sequence of values represents a
sine wave of amplitude –3.01 dB FS.)
This is added to the second component, an undithered
24-bit square wave of amplitude 1 LSB, made by switching
between the following:
000000 (0)
FFFFFF (-1 LSB)
This square wave is repeated at a low frequency. The
frequency is not critical but, for a sample frequency of
48 kHz, a rate of 250 Hz is normally used, as that makes the
signal synchronous with the AES3 channel status block of
192 samples. |
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