Benchmark DAC2 DX Manuel d'instructions télécharger pdf (Page 49)

DAC2 DX Instruction Manual Rev B Page 49

Graph Plot 3 - FFT 10 kHz

The 10 kHz FFT analysis is an excellent test for detecting sample clock jitter. Jitter will create

sidebands (unwanted tones) above and below the 10 kHz test tone. A jitter frequency of 1 kHz

would create two sideband tones; a lower sideband at 9 kHz, and an upper sideband at 11 kHz.

Similarly, a jitter frequency of 2 kHz would produce sideband tones at 8 kHz and 12 kHz. The

above plot shows no evidence of jitter-induced sidebands to a measurement limit of about -140

dBFS.

The -140 dB measurement limit is due to the SNR limitations of the Audio Precision 2700 test set,

and not the DAC2. Note the very low harmonic distortion; -114 to -116 dB 2nd harmonic (20 kHz),

and -120 to -122 dB 3rd harmonic (30 kHz). Please note that these are almost exactly the same

harmonic distortion levels that occur with a 1 kHz tone (see Graph Plot 4 - FFT 1 kHz). This

demonstrates that the DAC2 analog stages have the high slew rates required to pass high-

amplitude high-frequency signals without an increase in harmonic distortion.

The rise at 0 Hz is normal in an FFT analysis and is not an indication of noise. This 32k point FFT

analysis uses a Blackman-Harris window with 16x power averaging, and spans a frequency range

of DC to 32 kHz.

Audio Precision DAC2 - FFT 10 kHz, 0 dBr = 0 dBFS = 23 dBu

DAC2 - FFT 10 kHz.at27

ColorSweep Trace Line Style Thick Data Axis Comment Cursor1 Cursor2

1 1 Green Solid 4 Fft.Ch.1 Ampl Left *-114.636 dBr *-120.240 dBr

1 2 Red Solid 4 Fft.Ch.2 Ampl Right -116.765 dBr A -122.816 dBr A

-160

-140

-120

-100

-80

-60

-40

-20

-160

-140

-120

-100

-80

-60

-40

-20

-114.636

-120.24

0 32k2k 4k 6k 8k 10k 12k 14k 16k 18k 20k 22k 24k 26k 28k 30k

20.0391k 30.0587k

dx=10.0196 kHz

dy=-5.604 dB

1 2 ... 44 45 46 47 48 49 50 51 52 53 54 ... 72 73

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Benchmark DAC2 DX Manuel d'instructions Page 49

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