ds-xml-writing.md

@@ -14,4 +14,46 @@ The meat of the XML translation is in the ```<<``` operator of gdsDataObject def
 
 gdsdataum.cc:1371
 
-# transfer function subtypes
\ No newline at end of file
+# XML file binary array types and subtypes
+
+Key:
+
+c - complex value made of two floating point values
+f - a single floating point value representing a real value.
+
+They are followed by a byte size, so 
+c8 is an 8-byte complex, made of two 4-byte floating point values.
+
+Array contents are given as an ordered set.  
+
+Y - value of the array
+f - frequency associated with the array.
+
+If frequency is not included in the array, then it can be deduced by other provided information.  For example, if the frequencies form a linear series, they may be described by a start frequency and delta-frequency between buckets.
+
+Example
+
+A transfer function defined as 'c8 (f,Y)' means the array is of 8-byte complex values, each two values form an ordered pair with the first being the frequency associated with the value (as the real part of the complex number) and the second being the complex transfer function value.
+
+## Transfer functions
+
+As read by DTTXML:
+
+0: c8, (Y) Transfer function B/A.  Not apparently generated by DTT anymore.
+
+1: c8, (Y) Transfer function A, called STF (?).  Not apparently generated by DTT anymore.
+
+2: f4, (Y) Coherence B/A. Not generated
+
+3: c8, (f,Y) Transfer function B/A.  Generated in swept-sine tests, version 0.4.0
+
+4: c8, (f,Y) Transfer Function A.  Not generated.
+
+5: f4, (f,Y) Coherence B/A. Generated in swept-sine tests, version 0.4.0
+
+Proposed for 0.5.0:
+
+6: f8c8, (f,Y) Transfer Function B/A.  Frequency as double precision floating point, to replace subtype 3.
+
+7: f8f8, (f,Y) Coherence B/A.  Frequency as double precision to replace subtype 5.
+