Re: [LAU] first order ITU 5.1 preset for ambdec or second order stereo panner

Hello Hector, I delayed replying to this because the answers are not simple. I do have a 1st order ITU 5.1 preset, it's included at the end of this message. But you should consider the following. If you are panning individual sources into first order AMB then the results on a 5.1 rig could be inferior to what is possible using normal 5.1 panning. It depends a bit on what you expect - the 1st order images will always be more 'diffuse' than 'real' 5.1, OTOH, the imaging quality will be more constant as a function of position, and sound will appear less to come 'from the speakers'. First order to ITU 5.1 works well with signals recorded with an AMB microphone, but for panned material you want 2nd order. Regarding the stereo panner, it is equivalent to two mono panners, just with a different interface. But panning stereo into 2nd or higher order AMB may not give the result you expect. It is *not* a correct mapping from stereo to AMB - this is impossibles as essential information is lost when encoding to stereo (if it were possible then higher order AMB could be encoded without loss into two channels...). What happens is that you encode two source directions (the stereo speakers) correctly, and all the rest is just a linear combination of these. The AMB reproduction system will create two 'virtual speakers' for your stereo signal. The higher the order the more accurate this will be, but the acoustic result is just stereo. A central sound will be as 'fuzzy' as would be just using normal stereo reproduction. Even if your AMB rig has a speaker near to the central position it just won't be used, or very little, because you didn't pan anything there. How much this matters depends on how you use it. It will not be worse than stereo, but not better either while with higher order it _should_ be better. For first order the errors are relatively small for a normal stereo angle of 60 degrees. As order goes up, the maximum stereo angle that will give near to correct encoding gets smaller. Going above that will just lead to the 'stereo over ambisonics' situation explained above. For higher order, if you stereo signal is itself the result of panning individual sources, you should just skip the stereo step, and pan the same sources directly into AMB. Ciao, # AmbDec configuration # Written by MakeDec-0.7.0 at Tue Apr  7 00:04:23 2009 /description      5.0 First order decoder /version          1 /dec/hor_order    1 /dec/ver_order    0 /dec/freq_bands   2 /dec/speakers     5 /dec/coeff_scale  fuma /opt/input_scale  fuma /opt/nfeff_comp   input /opt/delay_comp   off /opt/level_comp   off /opt/xover_freq     300 /opt/xover_ratio    0.0 /speakers/{ #            id      dist     azim     elev     conn #----------------------------------------------------------------------- add_spkr    LS     1.500  110.000    0.000    alsa_pcm:playback_1 add_spkr    LF     1.500   30.000    0.000    alsa_pcm:playback_2 add_spkr    CE     1.500    0.000    0.000    alsa_pcm:playback_3 add_spkr    RF     1.500  -30.000    0.000    alsa_pcm:playback_4 add_spkr    RS     1.500 -110.000    0.000    alsa_pcm:playback_5 /} /lfmatrix/{ order_gain     1.00000  1.00000 #            W        X        Y #----------------------------------- add_row    0.42898 -0.32754  0.26524 add_row    0.22140  0.24055  0.37042 add_row    0.08957  0.21362  0.00000 add_row    0.22140  0.24055 -0.37042 add_row    0.42898 -0.32754 -0.26524 /} /hfmatrix/{ order_gain     1.00000  1.37000 #            W        X        Y #----------------------------------- add_row    0.67181 -0.19974  0.22776 add_row    0.40690  0.17925  0.23360 add_row    0.23133  0.29002  0.00000 add_row    0.40690  0.17925 -0.23360 add_row    0.67181 -0.19974 -0.22776 /} /end -- FA Io lo dico sempre: l'Italia è troppo stretta e lunga. _______________________________________________ Linux-audio-user mailing list Linux-audio-user(a)lists.linuxaudio.org http://lists.linuxaudio.org/mailman/listinfo/linux-audio-user