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Focusrite 18i20 DAC measurements

Blumlein 88

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Okay this is a Focusrite 18i20 (1st gen) audio recording interface. It has 8 microphone preamps, and line ins, ADAT, Word Clock, SPDIF over coax. I for this thread will focus on the DAC performance of the unit. Don't know that all Scarlett units function the same though probably similar. The unit does up to 96 khz, but I will focus on 48 khz results. Most measurements were done using an Antelope Audio Zen Tour ADC. The Zen Tour is several decibels quieter in noise and wider in dynamic range while having lower distortion than the 18i20 so it shouldn't corrupt results.

Noise floor is about -106 or -107 db. Not a world beater, but pretty good. Notably there are no idles tones, whistles or other anomalies. Here it is reproducing a -60 db 1 khz tone.

18i20 minus 60.png


The full scale 1 khz tone looks pretty good. THD is .00071% and THD+N is .00133%. Nothing to complain about here.

18i20 1khz.png


If you are wondering about hum take a look at 0-300 hz.

18i20 hum.png


The 12 khz J-test is pretty clean. Just a couple of spurs +/- 300 hz of the 12 khz tone. Those are lower than -120 db making them a non-problem.

18i20 jtest.png


The IMD test with 18+19 khz full scale tone is not bad at all. The 1 khz difference tone is more than -115db and other sum and difference tones are not very high in level.
18i20 imd.png





Here is a wideband look. Green is the -60 db 1 khz tone, and blue is - 4db of white noise. You can see this uses a half band anti-imaging filter. The rise above 30 khz is due to the sigma delta DAC chip in use. Don't worry about the little peak at 31 khz as that is an idle tone of the ADC. The Forte was used for this measurement.

18i20 Jurgen test.png

All in all pretty solid performance.
 
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