Thanks Fons and Jorn. writing the equation inside max6 I had several clipping problems with the decoding of a Soundfield ST450 signal, that has four matched line under single knob. With the “correct” equation I have a signal that falls within the correct dynamics like decoding into Blumlein fig-8 pair.
I think the W component of ST450 comes out scaled by sqrt2. I record the b-format in a single quadro file. the code: // max6 CodeBox - B-Format to MS to LR decoding W = in1; X = in2; Y = in3; Z = in4; // M = (sqrt2 * W) + X; // several clipping problem M = .5 * ((sqrt2 * W) + X); // without clipping S = Y; L = (M + S) / sqrt2; R = (M - S) / sqrt2; out1 = M; out2 = S; out3 = L; out4 = R; // fine Thanks. Bye. > ------------------------------ > > Message: 2 > Date: Thu, 15 Mar 2012 14:51:49 +0000 > From: Fons Adriaensen <f...@linuxaudio.org> > Subject: Re: [Sursound] question about simple equation > To: sursound@music.vt.edu > Message-ID: <20120315145147.ga22...@linuxaudio.org> > Content-Type: text/plain; charset=us-ascii > > On Thu, Mar 15, 2012 at 03:16:05PM +0100, Giuseppe Silvi wrote: > >> If cardioid pattern is descrbed by equation: >> >> cardioid = 1/2 ( 1 + cos Theta) >> >> and W equation is: >> >> W = 1 / sqrt2 >> >> replacing numbers with letters the equation should be this: >> >> cardioid = 1/2 ( sqrt2 W + X ) >> >> but for Mid-Side decoding from B-Format, where M is the same cardioid >> component, I often find this equation: >> >> M = sqrt2 W + X > > Which is the same, just 6 dB more gain. When using MS you will adjust the > relative gains of M and S anyway to obtain the desired width. You need to > do that also when using 'real' microphones for MS - in general they won't > have the same sensitivity. > > Ciao, > > -- > FA > > Vor uns liegt ein weites Tal, die Sonne scheint - ein Glitzerstrahl. > > > > ------------------------------ > > Message: 3 > Date: Thu, 15 Mar 2012 16:18:14 +0100 > From: J?rn Nettingsmeier <netti...@stackingdwarves.net> > Subject: Re: [Sursound] question about simple equation > To: sursound@music.vt.edu > Message-ID: <4f620836.3020...@stackingdwarves.net> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > On 03/15/2012 03:16 PM, Giuseppe Silvi wrote: >> Hi I'm Giuseppe from Rome, >> i apologize if my question could be trivial, but I have this problem in my >> mind to be solved. >> >> If cardioid pattern is descrbed by equation: >> >> cardioid = 1/2 ( 1 + cos Theta) > > this is a fact. > >> and W equation is: >> >> W = 1 / sqrt2 > > this is just a convention, which comes from the days of magnetic media. > i guess the observation was that in normal soundfield recordings, W is > usually a bit louder than X,Y, and Z, so in order to ensure optimal tape > saturation with maximal signal-to-noise ratio, W was reduced by 3dB > (that's the 1/sqrt2) before being recorded to tape. this way, you could > get roughly the same recording level for all 4 channels. > > the -3dB convention is technically not necessary any more (which is why > the new proposed ambisonic standard does away with it). but it makes a > lot of sense to keep the old WXYZ format as it is, in order not to break > all existing recordings. > > > > > -- > J?rn Nettingsmeier > Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487 > > Meister f?r Veranstaltungstechnik (B?hne/Studio) > Tonmeister VDT > > http://stackingdwarves.net > > > > ------------------------------ > > _______________________________________________ > Sursound mailing list > Sursound@music.vt.edu > https://mail.music.vt.edu/mailman/listinfo/sursound > > > End of Sursound Digest, Vol 44, Issue 11 > **************************************** _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound
