[Scipy-tickets] [SciPy] #1105: Logarithmic chirp frequency sweep incorrect

SciPy Trac scipy-tickets@scipy....
Sun Feb 7 19:49:41 CST 2010


#1105: Logarithmic chirp frequency sweep incorrect
-----------------------------------------+----------------------------------
 Reporter:  johntryan                    |       Owner:  somebody    
     Type:  defect                       |      Status:  needs_review
 Priority:  normal                       |   Milestone:  0.8.0       
Component:  scipy.signal                 |     Version:  0.7.0       
 Keywords:  chirp logarithmic frequency  |  
-----------------------------------------+----------------------------------
Changes (by warren):

  * status:  new => needs_review


Comment:

 The following patch makes a lot of changes to chirp:

 1. 'logarithm' can handle a more general range: f1 > f0 (instead of f1 >
 f0+1).
 Despite this fix, I think it would be better to drop the 'logarithm'
 method
 entirely.  The formula results in the actual instance frequency being f0+1
 at
 t=0, which is just wrong.  The new 'geometric' method is a more natural
 method to use.

 2. Added the 'geometric' method.

 3. Added the 'hyperbolic' method.

 4. Moved the handling of a polynomial specification of the frequency from
 chirp() to its own function, sweep_poly().  It really has a different API,
 so deserves its own function.

 5. Changed the formulas used by the 'quadratic' method, so that f0 is
 always
 the initial frequency and f1 is the final frequency in the sweep.

 6. Added tests.

-- 
Ticket URL: <http://projects.scipy.org/scipy/ticket/1105#comment:4>
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