# [sc-users] FMHEncode1/2 and ambdec

```Hello list,

```
Is it possible to use Fons Adriaensen's ambdec to decode FMHEncode1/2 encoded 2nd order signals? If so, which of FMHEncode's two scaling modes correspond to one (or two) of the 'N3D', 'SN3D' and Furse-Malham scalings available in ambdec?
```
I'll paste below the paragraph on scaling in the ambdec manual

Thanks,

Iain

```
In order to correctly use some of the options discussed below, the following must be understood.
```Ambisonic signals are traditionally scaled in a number of dierent ways.
```
For mathematical analysis it is very convenient to use the normalised form, meaning that each spherical harmonic has unity power when integrated over the sphere. This is called the 'N3D' form of Ambisonic signals. A close variation on this is the 'semi-normalised' or 'SN3D' form. This also has desirable mathematical properties, and is used by some existing software, for example the Ambisonic tools from IEM, Graz. The alternative to both, and widely used, is the so-called Furse-Malham form. This applies some gain factors to the signals so that they all have the same maximum level over all directions. The only exception is the pressure signal W which, for historical reasons, is attenuated by 3 dB. Many Ambisonic applications and audio les use the Furse-Malham representation. AmbDec allows to use all three representations, both for the input signals and for the matrix coecients. If the two settings are di erent, AmbDec will automatically apply the necessary gain factors to convert between them. So you can design a decoder matrix using the normalised form (which is usually less confusing, in particular for higher orders), and then use it with signals scaled according to the Furse-Malham standard. Important note: the normalised form used is always the 3-D one, even for an horizontal-only decoder. The reason for this is that all decoders are used in 3-D space | unless your speaker are in nite vertical line sources the rules of physical 3-D space apply, even when analysing a 2-D
```decoder.

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