The AIC26 audio output drivers in high power mode can be configured to drive a mono differential signal into a speaker load of 8-ohm minimum. The speaker load should be connected differentially between the HPR and HPL outputs.
Several options are possible for playback of DAC data in this case. If a stereo digital signal is available, this signal can be sent in normal stereo fashion to the audio DAC. The programmable digital effects filters can then be used to invert one channel, so that the signal applied across the speaker load is (LEFT + RIGHT), or effectively a mono-mix of the two channels.
A simple example of how to implement this inversion using the programmable filters is to set the coefficients as follows:
Left-ch coefficients (all-pass filter):
N0=32767, N1=0, N2=0, N3=32767, N4=0, N5=0, D1=0, D2=0, D4=0, D5=0
Right-ch coefficients (inverted all-pass filter):
N0=-32767, N1=0, N2=0, N3=32767, N4=0, N5=0, D1=0, D2=0, D4=0, D5=0
This provides no spectral shaping; it only inverts the right channel relative to the left channel, such that the signals at HPL and HPR are (LEFT) and (-RIGHT), with the signal across the speaker then being LEFT+ RIGHT.
In the general case when spectral shaping is also desired, the inversion can be accomplished simply by setting N0, N1, and N2 coefficients of one channel to the negative of the values set for the other channel. Note that the programmable filtering must be enabled by setting bit D1/REG-05H/Page2 to 1.