Following recent reports of Roon not being able to stream PCM content over 384 kHz, I decided to try it myself and confirm the issue. Sure enough, I’m not able to play tracks above that sample rate. Looking at the server logs, I found this:
07/02 10:26:44 Trace: [Topping ASIO] [zoneplayer/raat] StartStream Sooloos.Broker.Transport.RaatZonePlayer+Endpoint: StreamFormat(channels=2, bitspersample=16, samplerate=44100, isdts=False) => StreamFormat(channels=2, bitspersample=16, samplerate=44100, isdts=False) streamid=1975674922
07/02 10:26:44 Trace: [Topping USB Audio Device] [raatclient] SENT [6]{“request”:“setup”,“format”:{“sample_type”:“pcm”,“sample_rate”:44100,“bits_per_sample”:16,“channels”:2,“sample_subtype”:“none”},“wire_codec”:“flac”}
Note the “wire_codec” in the JSON above, which is set to “flac”. To me, this is a pretty clear indication that RAAT streams FLAC-encoded audio over the wire. This happens even if the source format is 44.1/16, as you can see in the logs, so it doesn’t seem to be related to saving bandwidth. This goes against the common knowledge that the server does all the necessary decoding and streams uncompressed PCM. Roon’s KB doesn’t specifically say that, but it does have this (my own highlight):
- Modest endpoint hardware requirements. This means endpoints don’t have to handle expensive DSP or content decoding–that will happen on the server. This means that many existing devices can add support for RoonReady without changing the hardware.
To be clear, I believe FLAC decoding does fall into the “modest requirements” category. I don’t have any issues with RAAT doing whatever it wants under the covers, as long as it uses lossless compression, and I am sure the little overhead stream decoding adds on the endpoint has absolutely no influence on sound quality. I do believe however that Roon needs to confirm that RAAT can send compressed streams over the wire, contrary to the aforementioned common knowledge.
Also, while I don’t really care about hi-res (having been advocating against it on many occasions), this seems to me like a serious regression, and the fact that it made its way into Roon is troubling. Whatever “smoke tests” they run to detect regressions before making such changes are not good enough apparently.
is it using flac because the server is detecting your network would struggle with PCM?