Espruino Wifi and SPW2430(microphone)

Ok, I think there are a few things here...

• 512 isn't the sample rate, it's the size of the buffer. Using 1024 could be a good idea though.
  
• The sample rate is in w.startInput - you're using 2000 currently (and the code you posted up is playing back at 8000). It'd be worth trying to use 4000 for both as a starting point (8000 might be possible, but for now let's not push it)
  
• You don't need analogWrite - you're trying to record so you want to input, not output.
  
• You definitely don't need E.FFT or any of that code with the FOR loops. FFT is something totally different to recording sound - and on Espruino at the moment you're going to struggle to record proper audio and do an FFT to pick out frequencies.
  
• Also appendFileSync has to find the file, open it, append, and close it - which can be quite slow. E.openFile is probably better.
  
  

Something like this should work:

var spi = new SPI(); 
spi.setup({mosi:B15, miso:B14, sck:B10});
E.connectSDCard(spi, B1);
console.log(require("fs").readdirSync());
var f = E.openFile("X.raw","w");
var w = new Waveform(1024,{doubleBuffer:true,bits:16});
w.on("buffer", function(buf) {
  f.write(buf);
});
w.startInput(B0,4000,{repeat:true});

setTimeout(function() {
  w.stop();
  f.close();
},10000);