Alright, now we are entering a much more interesting (and cleaner) area. Because I assume that many WiiM Pro owners are intending to use it mostly as a digital hub, paired with a much better DAC than what we have seen above. (in fact, you all have to!). These next tests have all been done without A/D conversion and are 100% in the digital domain. I used either REW tone generator for S/PDIF inputs, or WAV test files tones from the Audio Precision’s tone generator, then played through the WiiM Home App, or Roon. Results are directly recorded through S/PDIF with the ADI-2/4 Loopback.

Note: To state the obvious, zero difference has been observed between wired LAN and Wi-Fi connection (literary no reason there would). All tests have been done with Wi-Fi.

Let’s start with the regular main (Wi-Fi) input:​

Total Harmonic Distortion + Noise (SINAD) – 24b/44.1/192kHz

As we might expect from any decent unit, we got a textbook, absolutely perfect 1Khz signal, with distortion and noise out of this world. Nothing to worry about if you plan to use the WiiM Pro that way. The rest will be up to your own DAC.

By the way, just for peace of mind, this is how the SMPTE IMD looks like :​

Intermodulation Distortion SMPTE – 24b/44.1kHz​

Chromecast
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Since the WiiM Pro does have a Google Chromecast bluit-in, that uses different protocols than the WiiM App, we have to check its specific behaviour. To do so, I used a 44.1kHz 0dBFS sine wav, played through Roon (and WiiM Pro Chromecast as a Roon Endpoint). We got this:​

Total Harmonic Distortion + Noise (SINAD) – 24b/44.1/96kHz

Note: This test has been done again after the latest update. Before that, Chromecast’s performance was much worse (see there).​

S/PDIF pass-trough
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I also checked both optical and coaxial outputs, hardly trying to find any difference…​

Total Harmonic Distortion + Noise (SINAD) – 24b/48kHz

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Note: I have read and heard some early adopters complaining about the S/PDIF showing some delay, for instance when used with a TV optical output. I noticed nothing of the sort (LG OLED C2), so my guess is that it has been fixed since.

Speaking about it, here are the jitter plots for both:​

Jitter Optical – 24b/48khz

Jitter Coaxial – 24b/48kHz