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This commit is contained in:
Michael Hayes
2011-08-30 23:21:40 +00:00
parent 247e788f75
commit 020a0d55d7
1 changed files with 10 additions and 3 deletions
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extra/tweeter.h
+10 -3
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@@ -15,10 +15,17 @@ typedef uint8_t tweeter_period_t;
typedef uint8_t tweeter_velocity_t;
typedef uint8_t tweeter_scale_t;
/* Could calculate scale divisors at run time. 2^(1/2) is approx
/* We could calculate scale divisors at run time. 2^(1/2) is approx
1.0594631. A reasonable rational approximation is 267/252 =
1.0595238. Let's save memory and provide a macro to compute the
divisors. */
1.0595238.
Let's save memory and provide a macro to compute the
divisors. There is only 8 bits per note so the maximum POLL_RATE
is 255 * 82.41 = 21014 Hz. If we use a lower rate then the divisors
become less accurate, especially at the higher frequencies. For example,
with C5, f = 523 Hz, and if POLL_RATE = 10000, then the divisor is 19
giving a generated frequency of 526 Hz.
*/
#define TWEETER_DIVISOR(POLL_RATE, FREQ) (POLL_RATE / FREQ + 0.5)