A very interesting article on the Roon Labs Community forum (Roon Labs) discussed a “watermark” added by Universal Music Group (UMG) and the watermark affects the sound quality of the music being streamed. UMG makes up approximately 25% of the content in online catalogs and its labels include Interscope, The Island Def Jam, Universal Republic, Verve, GRP, Impulse!, Decca, Deutsche Grammophon, Geffen, etc. UMG uses the watermark for copyright enforcement. According to the post by Matt Montag, a software engineer at Spotify (mattmontag): “UMG uses a spread spectrum watermark, a technique explained in detail in this Microsoft research paper. The watermark scheme modulates the total energy in two different bands, 1khz to 2.3 khz and 2.3 to 3.6 khz. The energy is concentrated in the most perceptually sensitive frequencies because that makes it more difficult to attack or remove without significant audible distortion.
The energy is increased or reduced in 0.04 second blocks. The result can be characterized as a fluttering, tremolo sound. Listen closely to the original vs. watermarked audio samples and try to focus on the 1 khz to 3.6 khz noise range. It helps to wear headphones in a quiet environment.”
There is quite a bit more information in the aforementioned post including a comparison of samples of lossless original and watermarked files.