Audio Alchemy DTI Plus 音響魔術師時基校正器

音響魔術師 Audio Alchemy DTI Plus 時基校正器

AUDIO ALCHEMY DTI PLUS

JITTER ANALYSIS: CD TRANSPORT-TO-DAC VIA AUDIO ALCHEMY DTI PLUS 

One of many ‘little black boxes’ in the Audio Alchemy range, the DTI Plus offers inputs optical sources and provides a single coaxial output. Crystal’s evergreen CS8412 interface chip is run in ‘test mode’ with its free running PLL (Phase Locked Loop) offering jitter rejection beyond its 20kHz bandwidth. AA then provides a second stage of dejittering with a discrete crystal-based PLL that has a claimed bandwidth of just 5Hz. Once activated, a yellow LED lights up on the black fascia. 

This master oscillator is used to re-clock the CS8412’s digital output via a D-type flip-flop and buffer. In practice, however [Fig 1a and 1b], the common ground by its AC-coupled Input and output aggravates a massive increase in fundamental data induced jitter (13) and random noise (14) at frequencies well beyond the 5Hz suggested in AA’s literature. By way of comparison, a figure of 12304ps is nearly 100-times higher (worse) than that incurred by the best of today’s budget CD players. 

In reality the bandwidth of the crystal PLL must be several hundred Hertz because, via the optical input at least, the suppression of jitter only starts to take hold beyond the 3rd (15) and 5th (16) harmonic sidebands. If only the DTI Plus had been a transformer-coupled unit, then this unhappy result may well have been avoided.

Origin 

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Description 

Fundamental
3rd Harmonic
5th Harmonic
7th Harmonic
9th-11th Harmonic
Weighted Total

Peak-to-peak Jitter
Coaxial
12287ps(13)
459ps
263ps
298ps
207ps
12304ps

Optical
1869ps
205ps(15)
142ps(16)
165ps
1021ps
1895ps
Written By

Cyrus

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