As promised, here are the measurements of my desktop Gigabyte Gaming B8 motherboard powered by an i7 CPU:
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It makes lofty claims of audiophile sound:
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I will be testing its headphone performance later.
First, let's start with our usual dashboard at full volume (default was 65%):
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We get decent output compared to my laptop but still shy of 2 volt I like to see.
SINAD is a few dB worse than my laptop! As I always do, I knocked down the level gradually and at -6 dBFS, the performance is much improved:
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That's 14 dB higher SINAD! Alas, now our output voltage has fallen way down to just 0.67 volts RMS.
Frequency response is ruler flat to 17 kHz:
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At 22 khz, we have -3.4 dB droop. I like to see flat response to 20 kHz.
This is how it does on jitter and noise:
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Lots of spikes visible although levels at -120 dB are most likely not audible.
Let's look at intermodulation distortion (IMD) versus level. We use IMD test because it can detect non-linearity without having to have wide capture bandwidth to gather higher frequency harmonics as THD requires. In this case, I am using the SMPTE dual tone which is pretty sensitive to low frequency distortion:
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She starts doing well, matching dedicated external DACs but then goes nuts right at -35 dBFS but eventually recovers at -15 dB. In that region it is much worse than my laptop (in pink).
Let's analyze that by looking at the spectrum, first at -40 dB where response is well behaved:
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On the left you see our composite waveform. it is a 60 Hz tone that is being modulated by the 7 kHz tone (shown as solid band because they are too close together). The spectrum on the right shows them nicely separated (the two peaks).
Here is what we get at -30 dB where things should be getting better (due to better SNR), not worse:
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Focusing on the spectrum, we see a rise in our base noise floor (below 60 Hz tone) accompanies by harmonics of our 60 Hz which now spray throughout the spectrum.
I changed the frequency to 70 Hz but the same outcome remained so it has nothing to do with power supply.
There is definitely a design mistake here which is also visible in some desktop DACs but is much worse in this instance.
Let's look at linearity:
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The higher output voltage helps it do a lot better than my laptop. Strangely though there is some positive offset as low as -43 dBFS or so. Eyeballing this, looks like we have good linearity up to CD's 96 dB dynamic range.
Speaking of dynamic range, I decided to start showing this from here on since manufacturers always advertise it (as SNR):
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Even though it misses its 120 dB spec, it is still good at 107 dB.
Summary
We see more design issues here than on my HP Laptop. Peak performance is better but with that comes some anomalies such as mid-level rise in intermodulation distortion, and jitter.
Clearly we need to be measuring these PC subsystems to find the real jewels out there. I am open to building a case-less PC if people can loan their motherboards for testing.