Ask questions to Audio insider Sir Terrence

[Teazle]

Sir Terrence,

Thanks for your fascinating and informative posts on this forum. Picking up the thread re: multichannel audio as it promises to take over from stereo, I have a question about 5.1 vs. 7.1 surround.

People say that a true 7.1 recording played on a 7.1 setup is more immersive, more “surround-sounding” etc. than the same recording downmixed to 5.1 and played back on a 5.1 setup. Is there any way to quantify the difference to make such claims precise?

After all, 7.1 is 33% more channels than 5.1. But it seems doubtful to me that the “surroundedness” of 7.1 is 33% better. Is there some objective / scientific way to settle the matter? E.g. is there a way to measure (given some ideal speaker setup and listener position) the surround radius apparent to the listener, so it could be checked just how much wider a surround experience 7.1 offers? With 7.1 you can position a sound more precisely (since you can stick a sound exactly at x o’clock if a speaker happens to be there and the more speakers you’ve got the more likely it is that a speaker will be at x o’clock) but how much more accurately can the sound-field be manipulated?

No doubt 7.1 is better than 5.1; I’m just curious whether as far as surround sound effects go, 5.1 represents a point of diminishing returns.