# Re: equal loudness calculation

At 12:54 Uhr +0200 18.04.2005, Jose-Javier Lopez wrote:
``` in this case, I don't want to filter a sound, but simply scale its
amplitude.
Or is there a way to make the formula itself efficient by
implementing it as a filter?
```
```If you have your data in freq domain, just use the equation for weighting.
In this case you don't need to filter in time domain.
```
`ok, that seems good.`

`if anyone else needs it, here is the formula mapping freq to amp:`

```(
var k = 3.5041384e16;
var c1 = pow(20.598997,2);
var c2 = pow(107.65265,2);
var c3 =  pow(737.86223,2);
var c4 = pow(12194.217,2);```

```{|f|
var r = pow(f,2);
var m1 = pow(r,4);
var n1 = pow(c1 + r, 2);
var n2 = c2 + r;
var n3 = c3 + r;
var n4 = pow(c4 + r, 2);
var level = k * m1 / (n1 * n2 * n3 * n4);
sqrt(level)
};```

`)`

`JJ`

```----- Original Message -----
From: "Julian Rohrhuber" <rohrhuber@xxxxxxxxxxxxxx>
To: <AUDITORY@xxxxxxxxxxxxxxx>
Sent: Monday, April 18, 2005 12:18 PM
Subject: Re: [AUDITORY] equal loudness calculation```

>This is the analitic equation for A-Weighting.

http://www.beis.de/Elektronik/AudioMeasure/WeightingFilters.html#A-Weighting

` thank you, this is quite exactly what I was looking for.`

Just, pass it to Z domain and use "a" and "b" coef. in a IIR filter.
``` in this case, I don't want to filter a sound, but simply scale its
amplitude.
Or is there a way to make the formula itself efficient by
implementing it as a filter?```

`Very efficient !`

`JJ`

```----- Original Message ----- From: "Julian Rohrhuber"
<rohrhuber@xxxxxxxxxxxxxx>
To: <AUDITORY@xxxxxxxxxxxxxxx>
Sent: Tuesday, April 12, 2005 4:25 PM
Subject: [AUDITORY] equal loudness calculation```

```  I'm looking for a computationally efficient way to do a frequency
dependent amplitude compensation. The emphasis is much less accuracy
(especially not for different loudness levels) but more a reasonable
approximation - maybe a polynomial.```

`  Any hints?`

`  --`

`  .`

` --`

` .`

`--`

`.`