Update the default HRTF

The sample rate is now 48khz to match the library's default sample rate, and
increased the FIR length to 64 points from 32.

alsoftrc.sample

@@ -139,7 +139,7 @@
 #  Specifies the impulse response size, in samples, for the HRTF filter. Larger
 #  values increase the filter quality, while smaller values reduce processing
 #  cost. A value of 0 (default) uses the full filter size in the dataset, and
-#  the default dataset has a filter size of 32 samples at 44.1khz.
+#  the default dataset has a filter size of 64 samples at 48khz.
 #hrtf-size = 0
 
 ## default-hrtf:

docs/hrtf.txt

@@ -73,9 +73,7 @@ calculation (ie. left = angle, right = 360-angle).
 The actual coefficients follow. Each coefficient is a signed 24-bit sample.
 Stereo HRTFs interleave left/right ear coefficients.  The HRIRs must be
 minimum-phase.  This allows the use of a smaller filter length, reducing
-computation.  For reference, the default data set uses a 32-point filter while
-even the smallest data set provided by MIT used a 128-sample filter (a 4x
-reduction by applying minimum-phase reconstruction).
+computation.
 
 After the coefficients is an array of unsigned 8-bit delay values as 6.2 fixed-
 point integers, one for each HRIR (with stereo HRTFs interleaving left/right