break up into crates again

engine/time/time_sample_rate.rs

@@ -0,0 +1,23 @@
+use crate::*;
+
+/// Audio sample rate in Hz (samples per second)
+#[derive(Debug, Default)] pub struct SampleRate(AtomicF64);
+impl_time_unit!(SampleRate);
+impl SampleRate {
+    /// Return the duration of a sample in microseconds (floating)
+    #[inline] pub fn usec_per_sample (&self) -> f64 {
+        1_000_000f64 / self.get()
+    }
+    /// Return the duration of a sample in microseconds (floating)
+    #[inline] pub fn sample_per_usec (&self) -> f64 {
+        self.get() / 1_000_000f64
+    }
+    /// Convert a number of samples to microseconds (floating)
+    #[inline] pub fn samples_to_usec (&self, samples: f64) -> f64 {
+        self.usec_per_sample() * samples
+    }
+    /// Convert a number of microseconds to samples (floating)
+    #[inline] pub fn usecs_to_sample (&self, usecs:   f64) -> f64 {
+        self.sample_per_usec() * usecs
+    }
+}