ANSI S1.11.2004 Octave-Band Filter implementation
That's actually rather simple.
A little bit of trial and error will do the trick. The standard specifies upper and lower limit for the transfer function of the filter. So you can just try a normal Butterworth bandpass and see what happens.
The picture below shows a 3rd octave design at 1kHz and a sample rate of 48 kHz. A 2nd order bandpass isn't quite a good enough for class 1 limits, but a 3rd order does the job just fine. The 4th (and higher) order works as well.
Once you have a design that works at 1kHz, you can apply the same design to every other center frequency as well. At very high frequencies you will see some bilinear frequency distortion. Depending on your application you want to adjust for this or not.
Things to tweak are filter order, filter type and exact location of the corner frequencies. In the example the &quot;nominal&quot; corner frequencies worked just fine.