ADC16 Instruction Manual
Page 31
the converter IC. These high-frequency signals are a result of crosstalk between digital and analog
signals, and may have high amplitudes in a poorly designed system. Under ideal (low jitter)
conditions, a digital anti-alias filter may remove most of this unwanted noise before it can alias
down into lower (audio) frequencies. These crosstalk problems may not become obvious until jitter
is present.
Stop-band attenuation can be measured very easily by sweeping a test tone between 24 kHz and
at least 200 kHz while monitoring the output of the converter.
Put UltraLockDDS™ converters to the test
We encourage our customers to perform the above tests on UltraLockDDS™ converters (or let your
ears be the judge). There will be absolutely no change in performance as jitter is added to any
digital input on an UltraLockDDS
™
converter.
Try the same tests on any converter using conventional single or two-stage PLL circuits. Tests
should be performed with varying levels of jitter and with varying jitter frequencies. The results will
be very enlightening. Jitter related problems have audible (and measurable) effects on ADC and
DAC devices. Practitioners of Digital Audio need to understand these effects.
Is Jitter Elimination Possible?
Interface jitter will accumulate throughout even the most carefully designed digital audio system.
Fortunately, interface jitter can only degrade digital audio if it affects the sampling circuit in an
analog-to-digital or digital-to-analog converter. Any attempt to cure jitter outside of an ADC or
DAC (for example, with a low-jitter master clock) will prove expensive and, at best, will only
partially reduce jitter-induced artifacts. Dedicated clock signals (word clock, and super clock, etc.)
are often distributed to A/D converters and D/A converters in an attempt to reduce jitter. Again,
these are only partial solutions because jitter even accumulates in these clock distribution systems.
Furthermore, a poor quality master clock generator can degrade the performance of the entire
system, if converter performance is dependent upon reference clock quality. Jitter free ADCs and
DACs are the only true remedy to ill effects of jitter. UltraLockDDS™ converters are jitter immune
under all operating conditions (they will never add audible jitter induced artifacts to an audio
signal).
UltraLockDDS™ Capabilities
UltraLockDDS™ converters cannot undo damage that has already been done. If a converter with a
jitter problem was used to create the audio signal, then there is nothing that can be done to
remove the damage. Jitter-induced sidebands are extremely complex and cannot be removed with
any existing audio device. It is therefore important to attack jitter at both ends of the audio chain.
The ADC16 is a great start.
