Re: [Audacity-quality] ERB scale

[Steve t. F. <ste...@gm...>]

On 31 August 2015 at 16:18, James Crook <cr...@in...> wrote:
> On 31/08/2015 16:00, Peter Sampson wrote:
>
> Hi Paul,
>
> I've been doing my best to update the page in the 2.1.2 Manual
> for Spectrograms Preferences:
> http://manual.audacityteam.org/man/Spectrograms_Preferences
>
> I got fairly stuck on the various Scale and Algorithm settings, but ploughed
> ahead with Wikipedia as "my friend" - so it *will* need a fair bit of
> editing
> in those two sections.
>
> In particular I note that Wikipedia refers to:
>  "equivalent rectangular bandwidth or ERB"
>
> On this basis it seems to me that perhaps your nomenclature for ERBS
> is tautologous in its use of the final S for scale - i.e. a scale which is
> ERB
> Scale. And thus the  name for this scale might be better as simply "ERB".
>
> And this is an allowably fixable item under semi-freddo.
>
> Not just allowable.  If these kind of changes are wanted/valid/correct,
> positively encouraged.
>
> Later, in Frozen, it's more locked down.  P1 fixes in Frozen are always
> automatically OK.  P2s are generally good, but ask first.
>
> The RM.
>

I've been looking at this to see if I can help Peter with it, and
there is something very confusing here:

The Spectrogram "preferences" and track "settings" refer to "Scale",
which I think suggests that it is referring to the scale of the
vertical track ruler. However, the units of the vertical ruler are not
the units of the scale.

Example:
This image from Wikipedia indicates that 3500 Hz is approximately 2000
mel, https://upload.wikimedia.org/wikipedia/commons/a/aa/Mel-Hz_plot.svg
yet in the track Spectrogram view, a frequency of 3500 Hz is shown
with a value of "3500" (Hz) on the vertical ruler, not "2000" (mel).

"1/f" is also confusing because the inverse of a large number is a
small number, but it is not shown that way.

Steve