Support overlapping FFT blocks

Now an arbitrary number of samples can be read and appended to the FFT
block. Old samples will be dropped such that only BLOCK_LEN samples
are in the memory buffer. Currently one half of the FFT block is
replaced per update.

src/config.rs

@@ -1,3 +1,6 @@
 // definitions for the FFT
 pub const BLOCK_LEN: usize = 512;
 pub const SAMP_RATE: f32   = 48000.0;
+
+// samples read from stdin per update
+pub const SAMPLES_PER_UPDATE: usize = BLOCK_LEN/2;

src/main.rs

@@ -1,6 +1,7 @@
 // vim: noet
 
 use std::process::exit;
+use std::collections::VecDeque;
 
 use byteorder::{NativeEndian, ReadBytesExt};
 
@@ -34,17 +35,24 @@ fn main()
 	println!("Done! Starting main loop…");
 
 	// array for samples directly read from stream
-	let mut samples = [0i16; config::BLOCK_LEN];
+	let mut samples: VecDeque<i16> = VecDeque::with_capacity(config::BLOCK_LEN);
 
 	// main loop
 	loop {
 
 		// read a block of samples and exit gracefully on EOF
-		for sample in samples.iter_mut() {
+		for _i in 0 .. config::SAMPLES_PER_UPDATE {
+			// avoid increasing the size of the deque
+			if samples.len() == config::BLOCK_LEN {
+				samples.pop_front();
+			}
+
+			// read a sample from the input
 			let res = stdin.read_i16::<NativeEndian>();
 
+			// if everything is ok, append it to the samples deque
 			match res {
-				Ok(s) => *sample = s,
+				Ok(s) => samples.push_back(s),
 				Err(e) if e.kind() == std::io::ErrorKind::UnexpectedEof => {
 					println!("End of stream. Exiting.");
 					exit(0);
@@ -53,7 +61,13 @@ fn main()
 			}
 		}
 
-		sigproc.import_i16_mono(&samples).unwrap();
+		// only run calculations if the deque has been filled enough
+		if samples.len() < config::BLOCK_LEN {
+			continue;
+		}
+
+
+		sigproc.import_i16_mono_from_iter(samples.iter()).unwrap();
 		sigproc.update_fft().unwrap();
 
 		let energy_bass   = sigproc.get_energy_in_band(   0.0,  400.0);

src/signal_processing.rs

@@ -1,5 +1,7 @@
 // vim: noet
 
+#[allow(dead_code)]
+
 use fftw::array::AlignedVec;
 use fftw::plan::*;
 use fftw::types::*;
@@ -88,6 +90,20 @@ impl SignalProcessing
 		Ok(())
 	}
 
+	pub fn import_i16_mono_from_iter<'a>(&mut self, mut iter: impl std::iter::Iterator<Item=&'a i16>) -> std::result::Result<(), &str>
+	{
+		for fft_samp in self.fft_input.iter_mut() {
+			match iter.next() {
+				Some(sample) => *fft_samp = *sample as f32,
+				None         => return Err("Too few samples in input.")
+			}
+		}
+
+		self.apply_window();
+
+		Ok(())
+	}
+
 	pub fn update_fft(&mut self) -> fftw::error::Result<()>
 	{
 		self.fft_plan.r2c(&mut self.fft_input, &mut self.fft_output)?;