Spotify lossless is apparently not lossless on Windows, but a fix might be coming soon

Spotify Lossless was finally unveiled after years of delays, speculations and rumours. However, YouTuber The Headphone Show did an excellent, in-depth investigation into the service and found out it isn't nearly as lossless as advertised. The test suite included a FLAC track downloaded from a verified source, which was pitted against Tidal, Qobuz and Spotify lossless.

On the hardware side, it included an APx555B Series Audio Analyser to measure inputs, which were routed through a Holo Audio Red DAC and measured for parity on DeltaWave. Tidal and Qobuz's output was bit-perfect, meaning the streaming service played the lossless file as-is without any compression. Spotify Lossless, on the other hand, could not replicate the exact file in its uncompressed form.

That said, the problem might not be entirely Spotify's fault. In Windows, Spotify has no direct interface with a DAC, meaning all audio must pass through the operating system, which can result in signal integrity loss. Tidal and Qobuz can directly output audio to a DAC, but Spotify can't, at least officially.

However, in an earlier Reddit AMA, a Spotify community manager said WASAPI (Windows Audio Session API) Exclusive Mode playback support is being worked on. It essentially allows applications such as Spotify direct access to an audio output device such as a DAC. 

While there isn't an exact or even tentative estimate of when it will arrive, one can rest easy knowing it is being worked on. One can only hope it comes faster than lossless audio. Till that happens, third-party solutions like FlexASIO and VB-CABLE Virtual Audio Device can also be used as a stop-gap solution.