How does it sound to you? It is difficult to understand how many speakers with flat frequency responses sound completely different to other speakers with flat frequency responses, yet they do and we accept that. But if a piece of electronics has a flat frequency response we seem to expect it to sound exactly the same as any other piece of electronics with a similarly flat frequency response? Perhaps it lies in the test method vs actual music? After all measuring a constant and equal signal across the whole frequency range is very different to measuring the dynamic nature of real music.
Because speakers are only flat in one direction, no matter how they are designed, but still must live in a three-dimensional space full of reflections and resonances. And speakers distinguish themselves by how much voltage they can take with respect to distortion and output.
CD players have only transports and DACs. If they have a flat response, they have a flat response. And nearly all of them produce a ~2-volt output with respect to 0dB FS.
Some of them roll off the top octave a bit and some don’t, depending on their filters. You have to be able to hear above about 16 KHz to notice this, of course. But those differences are far easier to see in measurements than in music.
If you can detect something in music that you think isn’t being measured, then the burden is on you to identify it in terms that can be discussed and explored. But first you’ll have to show that your detection ability (or that of whoever you are believing) is robust in the absence of prior knowledge of the devices under test.
Rick “much arm-waving; no testing” Denney