# Directstream Mk 2 observations

Awesome, thanks!

I’d like to see a test where you (or @Paul!) send a -60 dBFS 1 kHz sine from the digital generator to each DAC and then measure THD+N with a 22 Hz high pass and a 20 kHz low pass. From this we can determine dynamic range for each DAC. If you note the 0 dBFS output level for each DAC we can also calculate residual noise.

I’d also love to see a FFT of both DACs at the same output level. I like 2 mV for noise measurements as it is usually pretty close to -60 dBFS.

Here are some examples from DACs I’ve measured. Unfortunately I am not using an AP but consumer ADCs and REW are so good these days you can get amazing results with minimal investment.

DAC 1
0 dBFS = 1.23 V
dynamic range = 51.6 + 60 = 111.6 dB
residual noise = 1.23 x 10^(-111.6/20) x 10^6 = 3.2 uV

DAC 2
0 dBFS = 4.40 V
dynamic range = 61.9 + 60 = 121.9 dB
residual noise = 4.4 x 10^(-121.9/20) x 10^6 = 3.5 uV

DAC 3
0 dBFS = 3.83 V
dynamic range = 42.6 + 60 = 102.6 dB
residual noise = 3.83 x 10^(-102.6/20) x 10^6 = 28.4 uV

Both DAC 1 and 2 are very low noise. DAC 1 has a slightly lower absolute noise level than DAC 2 but DAC 2 has higher dynamic range because of the higher output level at 0 dBFS. Either of these DACs can be used without a preamp with sensitive speakers with no audible hiss. DAC 3 is much higher noise and would be less suited for use without a preamp.

And finally all three DACs compared at 2 mV output level on a common FFT. Here it is very easy to see that DACs 1 and 2 have very low and similar absolute noise levels, while DAC 3 clearly has much higher noise.

Michael

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