anchor.diff:     (bits-per-sample :initform +bits-per-sample+
                       :initarg :bits-per-sample
                       :accessor bits-per-sample)
  +   (extension-size :initform +extension-size+
  +                   :initarg :extension-size
  +                   :accessor extension-size)
      (frames :initform '()
              :accessor frames
              :initarg :frames)))
  
positive.code:                  (sample-rate (read-uint in 4))
                   (bytes-per-second (read-uint in 4))
                   (bytes-per-sample (read-uint in 2))
                   (bits-per-sample (read-uint in 4))
                   (data-id (read-tag in))
                   (data-size (read-uint in 4))
                   (value-range (expt 2 bits-per-sample))
  
negative.code:    (io :initform nil
             :initarg :io
             :accessor io)
     (fmt-size :initform +fmt-size+
               :initarg :fmt-size
               :accessor fmt-size)
     (num-channels :initform +num-channels+
                   :initarg :num-channels
                   :accessor num-channels)
  