ASRC gain issue using TDM mode in 2156x


We are using HW ASRC in TDM mode in processor ADSP21569 for converting TDM16 44.1K audio to TDM16 48K audio. Since we need only two channels to be upsampled and hence we use only one ASRC. We found that single ASRC on TDM16, inverts the TDM slots. Hence we send valid data in TDM slot 14 and 15 to ASRC. ASRC upsamples and sends the output in slot0 and slot1. ASRC output is connected to TDM SPORT from which we receive the data for audio processing. 

But we see that the ASRC output received in TDM SPORT buffer has a gain of x2. Hence if we give 0dB signal, ASRC operation results in saturation. We have to use input signal of -6dB to avoid saturation in ASRC. What could be the reason for this?

We had struggled quite a bit to get ASRC working. When we were using the SPORT sampling edge as rising edge, we were getting folded sine wave as output. (I am not able to attach pictures in this editor). We had to change SPORT sampling edge as falling to get proper sine wave.