;;; -*- syntax: common-lisp; base: 10; mode: lisp -*- ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;; ;;; File: panning.lsp ;;; ;;; Version: 1.0 ;;; ;;; Purpose: ;;; ;;; Get the constant power panning scalers for left and right ;;; channels given a degree from 0 (left) to 90 (right). ;;; ;;; Avoids the "hole in the middle" problem that occurs when ;;; trying to centre a signal in the middle of two speakers ;;; by "incorrectly" placing exactly half the full signal in ;;; both channels. ;;; ;;; The formulas are: ;;; ;;; Amp Left = (sqrt-2 / 2) * (cos(theta) + sin(theta)) ;;; Amp Right = (sqrt-2 / 2) * (cos(theta) - sin(theta)) ;;; ;;; where theta is the desired angle between left and right ;;; speakers expressed between +45 (left) and -45 (right). ;;; ;;; Note however that our degree argument to get-cpp-scalers ;;; is between 0 (left) and 90 (right) and that the function ;;; will return the scalers for left and right channels (in ;;; that order) as a 2-element list. E.g. ;;; ;;; (get-cpp-scalers 0) => (1.0 0.0) ;;; (get-cpp-scalers 45) => (0.70710677 0.70710677) ;;; (get-cpp-scalers 90) => (0.0 1.0) ;;; ;;; In the middle then, when theta is 0 and our degree 45, ;;; the scalers for left and right channels will be 0.707 ;;; both, not 0.5. ;;; ;;; See The Computer Music Tutorial, Curtis Roads, pp 459-461 ;;; for more details. ;;; ;;; Author: Michael Edwards - michael@ccrma.stanford.edu ;;; ;;; Creation date: January 25th 2001 ;;; ;;; \$\$ Last modified: 11:48:01 Tue Jul 5 2011 BST ;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; (let ((magic (/ (sqrt 2) 2))) (defun get-cpp-scalers (degree) ;; although we (in clm) specify the degree from 0 - 90, for the sake ;; of the calculation it's from -45 to 45 with 0, not 45, being the ;; centre. (let* ((radians (degrees-to-radians (- 45.0 degree))) (cos (cos radians)) (sin (sin radians))) (list (* magic (+ cos sin)) (* magic (- cos sin)))))) ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; (let ((2pi360 (/ (* 2 pi) 360))) (defun degrees-to-radians (degrees) (* degrees 2pi360))) ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;; EOF panning.lsp