[PD] isosonic curves : level the perceptual loudness of different pitches

Ed Kelly morph_2016 at yahoo.co.uk
Fri Feb 9 15:59:16 CET 2007

Hi Alex, all

...but PDs dB goes to 0, because we have to have the numbers following the same scheme - so that 0 means 0 always I think. Industry uses dBFS (deciBel Full Scale) because it is measuring the  signal against the full scale from -96dB in 16bit recordings to  0dB (all bits used). 

Basically, the reason for dB is that our ears hear sound in a non-linear fashion, rather like frequency in fact which is why we have [mtof]

Each drop of (n)dB will be heard as the same amount of reduction in loudness, whereas every linear drop is different perceptually. So, if you have a signal at 96dBPD (-4dBFS) and you set it to 90dBPD (-10dbFS), the loudness will be heard to drop by the same amount as when you then set it to 84dBPD (-16dBFS). In fact, you have halved the amplitude twice, so it is a quarter of what it was, but each drop is heard as the same. This is the difference between amplitude (linear [*~ ]) and loudness (logarithmic)

...so you could relate dB to pitch accounting for the energy at different pitches quite simply, if you use inputs to [dBtorms] and [mtof] in some form of inverse-proportion.

[*~ ]


Alexandre Quessy <listes at sourcelibre.com> wrote: Hi all,

2007/2/8, Frank Barknecht :
> Yes, it's new. You could use the [list-len] abstraction from
> [list]-abs instead, but you need to check out an older version,
> because the newest one just wraps [list length].

zexy's [length] also does the job, as far as I know.

As I can see, I am still very bad at using the dB unit for audio
amplitude... Anyone has a rule of thumb for this ? Should I use dB
with a simple ADSR filter, let say ? I know that if you use them, -6
dB is somewhat half as loud and +6 dB is twice as loud. Great. Now, in
pd, 100 is unity while in the industry, the consoles use 0 for unity
level. 0 in pd is minus infinity, as far as I know. Now, what is
usable ? After a drop of a few dB, we don't hear anything.
Perceptualy, I find the standard [*~] range of numbers more linear
than using the dB scale.

So, the RMS kind of mean the actual amplitude of the vibrating
membrane of the speaker... http://en.wikipedia.org/wiki/Audio_power :
hence we use [- 100] [dbtorms] for the conversion. Anything else one
should know ?

Perhaps I should put it somewhere on puredata.org after. :)
Alexandre Quessy

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