The difference between mono and stereo
I had a conversation with an engineer about recording an acoustic piano in mono and then making it stereo. Of course my first question was, Why don't you record it in stereo? He thought it would be easier to record the piano with one mic, copy the file, then pan the original left and the copy of the file right. I explained that stereo does not work that way. After that encounter, I can across others who did not understand how to record in stereo. I decided to try to explain the difference between mono and stereo. Here we go!
When we go through our daily lives, we hear our world in stereo. This is because we have two ears. With two ears, we are able to close our eyes and still detect which direction sound is coming from. As we listen to a sound source, the way the sound source hits our ears helps us to figure out direction. If the waves hit both of our ears at the same time and at the same volume, we know that the source is right in front of us. If it is louder on our left side, we know that the sound is on our left side. The opposite is also true. We do not have to analyze this, our brain figures this out automatically. If we only had one ear, this would not be possible. There are other benefits to hearing in stereo, but we can cover that in another post.
Now that we understand the reason we hear in stereo, let's look at recording again. Just like the human body, our recording situation needs to have two inputs to record in stereo. Even if you are recording one instrument, you still need two inputs. Think of it this way, even the person playing an acoustic piano is experiencing a stereo performance. The lower notes are heard slightly louder on the left, and the higher notes are heard slighter louder on the right. One ear can't produce that experience, neither can one mic. The rule is, one mic for mono, two mics for stereo.