Marketing leads us to believe that AD/DA Conversion will improve with external synchronization/clocks. This is not the case.
It’s no mystery that multiple digital devices need common clock reference to communicate properly. Large studios need common (house clock) to communicate from device to device & room to room. But do personal project studios benefit from external synchronization?
The short answer is no.
I have yet to find any AD/DA Conversion/Audio interface that performs better while locked to external reference. (word clock, AES, video, SPDIF, TOS, ect.)
I judge conversion quality by three key specifications. (In general the lower the better.)
- Jitter – The deviation in or displacement of a digital signal. Small variations in a waveform.
- THD+N – Total harmonic distortion plus noise
- IMD – inter-modulation distortion is the unwanted amplitude modulation of signals containing two or more different frequencies in a system with nonlinearities.
In almost all cases a device locked to external reference will measure decreased performance in every one of these areas. (Found & not limited to Apogee, TC, Avid/digidesign, Lynx, AMS-Neve, M-audio, Prism, Aphex, Focusrite, Studer, ect).
Lynx Aurora – Analysis plots = http://flickr.com/gp/rhythminmind/iM9cr4
- Jitter – External = 2.3ns Internal = 1.1ns
- DA THD+N – External = .00046% Internal = .00040%
- DA IMD – External = .00039% Internal = .00037%
- AD THD+N – External = .00046% Internal = .00041%
- AD IMD – External = .00038% Internal = .00037%
Apogee AD-8000 – Analysis plots = http://flickr.com/gp/rhythminmind/98s814
- Jitter – External = 6.5ns Internal = 3.4ns
- AD THD+N – External = .00089% Internal = .00073%
- AD IMD – External = .00611% Internal = .00059%
DigiDesign 192 – Analysis plots = http://flickr.com/gp/rhythminmind/B99YUQ
- Jitter – External = 3.5ns Internal = 1.9ns
- DA THD+N – External = .00051% Internal = .00052%
- DA IMD – External = .00137% Internal = .00045%
- AD THD+N – External = .00093% Internal = .00093%
- AD IMD – External = .00195% Internal = .00070%
Lynx L22 – Analysis plots = http://flickr.com/gp/rhythminmind/C5w790
- Jitter – External = 6.3ns Internal = 1.2ns
- AD THD+N – External = .00047% Internal = .00038%
- AD IMD – External = .00066% Internal = .00031%
DigiDesign MBOX2 – Analysis plots = http://flickr.com/gp/rhythminmind/45UiBQ
- Jitter – External = 7.2ns Internal = 4.2ns
- DA THD+N – External = .00061% Internal = .00064%
- DA IMD – External = .00067% Internal = .00033%
- AD THD+N – External = .00094% Internal = .00084%
- AD IMD – External = .00085% Internal = .00055%
DigiDesign 888/24 – Analysis plots = http://flickr.com/gp/rhythminmind/f7c3Us
- Jitter – External = 2.7ns Internal = 1.8ns
- AD THD+N – External = .00146% Internal = .00117%
- AD IMD – External = .00205% Internal = .00092%