The problem is that I do not know how to send the audio signal to the Arduino. I am afraid serial port won't be fast enough.
Most people use analog.
- Would it be possible to simply feed the stereo headphone jack of my computer to the Arduino ? Just MONO.
Yes, and unless your signal is mono you can digitally-sum the left & right channels. (Mixing is done by summation and analog mixers are built around summing amplifiers.)
2.) There are some microphones for Arduino such as:
Electret – amplificateur de Microphone Stable, module MAX9814, contrôle automatique du Gain, MAX4466 | AliExpress
I have the SparkFun mic. It works OK but it needs slightly-loud sound and there is no sensitivity control. i.e. Louder than I normally listen to the TV. (I normally use a direct connection.*) I just bought it to experiment with.)
There are a few different kinds of microphone boards. The SparkFun version puts-out a biased audio signal, which is what you want for FFT. Some put-out a DC voltage proportional to the loudness and some put-out a logic-one when the volume is above a preset threshold. Some have automatic gain control which you may, or may not, want. (I build automatic sensitivity control into the software.)
Would it be possible to desolder the microphone and solder the line-out of my computer instead? This way I will benefit from the amplifier (opamp) and get the signal to the Arduino.
If you want to pick-up acoustic sounds with the a microphone, I'd recommend buying microphone board rather than "destroying" your computer.
If you want to use headphone-out or line-out, get a [u]Y-Splitter[/u] so you can connect speakers/headphones at the same time. (You won't be able to use the built-in laptop speakers because they cut-off when you plug something in.)
If you use a direct connection you'll need to bias the input at half the supply voltage. Without bias the Arduino can be damaged by the negative-half of the AC audio signal and/or the signal can be "damaged" distorted, and your readings will be distorted without the negative-half of the audio signal and that will totally foul-up your FFT. Since the bias is DC (zero-Hz) you can simply ignore the zero-Hz FFT bin. The standard bias circuit is attached to the bottom of [u]this post[/u].
I want to make one of these cool LED music equalizers
It's actually a spectrum analyzer effect. The MSGEQ7 is mis-named but I guess it's intended to be a visual effect built-into an equalizer.
- I've made a few sound-activated effects but I've never used FFT. My effects are just loudness or "beat" activated. I'm "thinking about" an MSGEQ7 effect but it will be variations of a color organ/light organ, not a spectrum analyzer.