[Noisebridge-discuss] Hearing augmentation

[Lamont Lucas]

Christoph Maier wrote:
> The really interesting problem is how to speed up or slow down the
> individual oscillation while not changing the time the entire sound
> takes. 
>
> Anyhow, what's that tool called again that makes every singer (even Ms
> Spears and Winehouse) sound pitch perfect?

Autotune.  A vocoder would work as well.

Here's a nice page that explains the difference between straight 
frequency shifting and Spectrum Shifting (aka Pitch Shifting):

http://www.cim.mcgill.ca/~clark/nordmodularbook/nm_spectrum_shift.html

The short version is that frequency shifting is easy, but you lose the 
harmonic relationships between the original frequencies, which would 
probably make it hard to pick out a birdsong someone was already used to 
hearing.  I think the easiest way to do it is to look for a single 
sideband implementation (SSB)

But you probably want spectrum/pitch shifting, the digital 
implementation of which involves storing audio samples in a delay line 
at the original rate, then playing them back at a faster rate.  


Check this out too:

http://www.dspdimension.com/admin/time-pitch-overview/