Phantom center correction, why ?


Although not described in the original stereo proposals, the 60° playback angle has become the standard over years. Sound engineers are using this configuration during the different stages of recording & production process.


You might not have this standard 60° configuration at home for different reasons: installation constraints, personal preference, use of acoustic crosstalk reduction (lower span angle improve effect robustness)


Any deviation from the standard configuration has an impact on the perceived tonal balance, especially for voices and instruments placed at the center of the soundstage. We need to come back to the principle of stereo imaging to understand this: 


Stereo imaging is based on the creation of phantom sources by controlling the output level of left and right speakers. To place sources at the center, the same signal is sent to both loudspeakers. As explained during our video on crosstalk reduction (here) this configuration creates a spectral modification compared to a real source that would be at the same position (this is because the sound waves from the left and right speakers will mix at each ear with slightly different delays and create comb filtering)

This spectral coloration is somehow mitigated by room reflections, but sound engineers themselves are largely compensating for this spectral coloration by applying filters during mixing. As they are doing this using the 60° configuration, what happen if you listen with a different configuration?

The graph below is showing the spectral deviation of a centered source for one individual when listening with 50 or 40° angle vs 60° reference in anechoic conditions:


As you can see the deviation are very significant, especially in the frequency region where the ear is most sensitive (2 to 4 kHz)

This anechoic condition is the worst case as no room reflections are smoothing the frequency response. In typical listening conditions the deviation will be lower but still significant.


Even if we all have a different hearing and a different perception of tonality, the hifi ultimate objective is to be as close as possible as the sound engineer’s conditions: this is why phantom center image deserves correction when your listening configuration deviates from the 60° standard.