hobbyist wrote:Room acoustic is always everywhere in the playback.
No. It isn't. This is stereo mic basics 101...
Try this mind-experiment: You have a piano recording made with two mics (in any arrangement you like), but you pan them both centrally. When you play that back on stereo speakers the piano sound will form a narrow image mid-way between the speakers.
How wide is the spread of 'room sound' across the image? *1
Now extend that to consider what happens if you pan the two mics out from the centre part way. What happens to the piano image now? *2
And the spread of room sound? *3
Now contrast that to what happens if you have an XY stereo array (let's say crossed cardioids for simplicity) a long way back from the piano in a big concert hall. How wide is the piano image? *4
And the spread of room sound? *5
And finally, move the XY array much closer to the piano and answer the same two questions:
How wide is the piano image? *6
And the spread of room sound? *7
Hopefully, you'll now realise that the width of all elements within a stereo image is dependent on many things, but especially the pan positions, and narrowing the image with pan pots affects the room sound image width just as much as the piano image itself.
*1 There is no spread: it's a paper-thin-narrow phantom centre image overlaying the (mono) piano sound.
*2 The piano image is no longer quite such a narrow central phantom image, and it will occupy a small amount of stereo width.
*3 The room sound will be as wide -- but no wider -- than the piano sound.
The visual equivalent is watching an old 4:3 format TV programme on a widescreen TV with black strips down each side.
To achieve full stereo width there needs to be around 16dB of level difference (or around 1.5ms of time difference) between the left and right channels, and that can't be achieved with part-panning. So the image width must always be smaller than the total stage width between the speakers.
*4 Very narrow, because the piano physically occupies only a narrow chord of the mic array's whole stereo acceptance angle.
*5 The room sound spreads across the entire stereo image because it occupies the mic arrays complete stereo acceptance angle.
Again the visual equivalent is a widescreen image on a widescreen TV with a small piano at the centre of the image.
*6 The piano now spreads much more widely across the stereo image because it fills a much larger chord within the mic array's stereo acceptance angle.
*7 The room acoustic still fills the full stereo width because it still occupies the mic arrays complete stereo acceptance angle.