diff --git a/src/main.c b/src/main.c
index 1224f71..7d4bd24 100644
--- a/src/main.c
+++ b/src/main.c
@@ -20,8 +20,11 @@
 #define IRP_SM 0
 #define IRN_SM 1
 
+// Actually one less, but this is also for timing.
+#define SAMPLE_DEPTH 128
+
 #define NUM_SAMPLES_BITS 10
-#define NUM_SAMPLES      (1 << NUM_SAMPLES_BITS)
+#define NUM_SAMPLES (1 << NUM_SAMPLES_BITS)
 static uint16_t irp_buffer[NUM_SAMPLES] __aligned(2 * NUM_SAMPLES);
 static int dma_ch_irp_rx;
 
@@ -68,7 +71,7 @@ static void init_pio_sm(pio_hw_t *pio, int sm, int rx_pin, int fb_pin)
 	pio_sm_restart(pio, sm);
 	pio_sm_clear_fifos(pio, sm);
 
-	pio->txf[sm] = 126;
+	pio->txf[sm] = SAMPLE_DEPTH - 2;
 	pio_sm_exec_wait_blocking(pio, sm, pio_encode_pull(false, false));
 	pio_sm_exec_wait_blocking(pio, sm, pio_encode_mov(pio_x, pio_osr));
 
@@ -98,11 +101,11 @@ static bool read_sample(int *sample)
 	int neg = irn_buffer[tail] << 16;
 	tail = (tail + 1) % NUM_SAMPLES;
 
-	int s = pos - neg;
+	int s = neg - pos;
 
 	static int dc;
-	dc += (s - dc) >> 16;
 	s -= dc;
+	dc += s >> 16;
 
 	*sample = s >> 16;
 	return true;