KEY 15, CHR$(0) + CHR$(&H2D)
ON KEY(15) GOSUB terminate
KEY(15) ON
DIM tata(8192), x(4096)
REM to put in scaling constant (sc), sample rate (sr), and number
    ' of points (fft) which can be 256, 512, 1024, 2048, or 4096 max
sc = .002
sr = .362
fft = 4096
redo:
CLS
REM this loop clears previous plots
FOR i = 1 TO 23
LOCATE i, 1
PRINT "                                                                          "
NEXT i
CLOSE #1
SCREEN 9
COLOR 7, 1
LOCATE 1, 1
PRINT "input text file name"
INPUT file$
OPEN file$ FOR INPUT AS #1
nn = fft
FOR i = 1 TO n
	tata(i) = 0: NEXT
FOR i = 1 TO nn
INPUT #1, x(i)
 sy = sy + x(i)
 sx = sx + i
 sx2 = sx2 + i ^ 2
 sxy = sxy + i * x(i)
 NEXT i
nn = fft
n = 2 * nn
CLS
a1d = sx2 - sx ^ 2 / nn
a1n = sxy - sx * sy / nn
a1 = a1n / a1d
a0 = sy / nn - a1 * sx / nn
FOR i = 0 TO nn - 1
x(i) = x(i) - a1 * i - a0
NEXT i
	FOR j = 2 TO n STEP 2
	tata(j - 1) = x(j / 2)
	NEXT j
VIEW (150, 40)-(600, 320), , 1
CLS
LOCATE 23, 40: PRINT "time"
WINDOW (1, -10)-(nn, 10)
FOR i = 1 TO nn
IF i > 1 THEN LINE (ip, sc * xp)-(i, sc * x(i))
ip = i: xp = x(ip)
NEXT
SLEEP 2
j = 1
FOR i = 1 TO n STEP 2
  IF j > i THEN
	 tempr = tata(j)
	 tempi = tata(j + 1)
	 tata(j) = tata(i)
	 tata(j + 1) = tata(i + 1)
	 tata(i) = tempr
	 tata(i + 1) = tempi
  END IF
 m = n / 2
SET1:
  IF m >= 2 AND j > m THEN
	  j = j - m
	  m = m / 2
	  GOTO SET1
	END IF
 j = j + m
NEXT i
 mmax = 2
SET2:
   IF n > mmax THEN
	 istep = 2 * mmax
	 theta = 6.28318530717959# / mmax
	 wpr = -2! * SIN(.5 * theta) ^ 2
	 wpi = SIN(theta)
	 wr = 1!
	 wi = 0!
	FOR m = 1 TO mmax STEP 2
	  FOR i = m TO n STEP istep
	   j = i + mmax
	   tempr = wr * tata(j) - wi * tata(j + 1)
	   tempi = wr * tata(j + 1) + wi * tata(j)
	   tata(j) = tata(i) - tempr
	   tata(j + 1) = tata(i + 1) - tempi
	   tata(i) = tata(i) + tempr
	   tata(i + 1) = tata(i + 1) + tempi
	 NEXT i
	   wtemp = wr
	   wr = wr * wpr - wi * wpi + wr
	   wi = wi * wpr + wtemp * wpi + wi
	 NEXT m
   mmax = istep
   GOTO SET2
  END IF
''''''''''''''''''''''''''''''
SECONDLOOP:
CLS
VIEW (150, 40)-(600, 320), , 1
WINDOW (1, -140)-(nn, 20)
FOR i = 2 TO nn STEP 2
ta = sc ^ 2 * (tata(i) ^ 2 + tata(i - 1) ^ 2) / (nn / 2) ^ 2
db = 10 * .4343 * LOG(ta): ' .4343 to convert from natural log to base 10 log
IF i > 2 THEN LINE (ip, dbp)-(i, db)
ip = i: dbp = db
PSET (10 * i, 20)
PSET (10 * i, 0)
PSET (10 * i, -20)
PSET (10 * i, -40)
PSET (10 * i, -60)
PSET (10 * i, -80)
PSET (10 * i, -100)
PSET (10 * i, -120)
NEXT
LOCATE 11, 1
PRINT "          dB    "
LOCATE 7, 35: PRINT "SPECTRUM ("; fft; "point FFT )"
LOCATE 3, 33
PRINT "Frequency (frac. of"; sr / 2; "Hz)"
LOCATE 3, 17: PRINT "20"
LOCATE 8, 16: PRINT "-20"
LOCATE 13, 16: PRINT "-60"
LOCATE 18, 15: PRINT "-100"
LOCATE 23, 15: PRINT "-140"
LOCATE 2, 29: PRINT "0.2"
LOCATE 2, 41: PRINT "0.4"
LOCATE 2, 52: PRINT "0.6"
LOCATE 2, 64: PRINT "0.8"
LOCATE 2, 76: PRINT "1."
CLOSE #1
waitps:
IF INKEY$ = "r" THEN GOTO redo
GOTO waitps:
terminate:
END