[Nyquist-users] Simple function to reverse a sound

[<dav...@sy...>]

Hi!

I wrote a very simple function to "reverse" a sound in time=2E It doesn't
run very quickly, but it might be useful for short sounds=2E I couldn't
think of any way to do it except extract all the samples to an array,
reverse the array, and convert it back to a sound=2E If there's a more
efficient way (other than writing it in C), please let me know=2E

If you think it might be useful, please feel free to add it to the
next release=2E It uses a "helper" function, 'array-reverse', since=20
there doesn't seem to be any function in Xlisp to do this=2E

David=2E

(defun array-reverse (a length)
    ;; Note: this function updates the input parameter
    ;; in place=2E If you don't want this, copy the array
    ;; to another variable first=2E
    (prog* ((mid (/ length 2)) (tmp nil))
        (if (equal (type-of a) 'ARRAY)
            (do ((n1 0) (n2 (1- length)))
                ((>=3D n1 mid) a)
                (setf tmp (aref a n1))
                (setf (aref a n1) (aref a n2))
                (setf (aref a n2) tmp)
                (setf n1 (1+ n1))
                (setf n2 (1- n2))
            )
            (return a)
        )
    )
)

(defun snd-reverse (s)
    ;; returns time-reversed sound (preserving sample rate and start=20
    ;; time), but doesn't operate on multi-channel sounds
    (if (soundp s)
        (prog* ((len (snd-length s NY:ALL)) (a (snd-samples s len)))
            (array-reverse a len)
            (return (snd-from-array (snd-t0 s) (snd-srate s) a))
        )
    )
)


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