[Sergedc]

Hi, 
 
I have a USB 5.1 sounds card based on CM108 chip which has a AC3/DTS internal hardware decoder. The sound card is HIFI360.cn HF-D1B.
 
When I play a movie, I have 2 options (using AC3filter):
1. Use AC3 encoder in AC3filter: the sound is encoded in AC3 format and passed on to the CM108 as SPDIF 5.1 48000. The hardware decoder of the sound card then decodes the DD5.1 and outputs it.
2. Don't use the AC3 encoder in AC3filter: the sounds is send as PCM 5.1 48000 to the sound card. 
 
The sound card is connected to the AMP with RCA cables. In both cases, I end up with 5.1 sounds arriving to my amp and to my speakers. But in case 1 (Use AC3 encoder), the sound is at normal volume (and hence very clear). But in case 2 (PCM 5.1), the volume is much reduced and I have to push my amp to insanely high level which deteriorates the sound.
 
Any idea why this is / what is happening?
 
All other config are the same between the two test. Basically, only unticking the AC3 Encoder, directly reduces the sound volume.
 
Thanks, 
Serge

 

[Sergedc]

I found the reason. When connected via USB, 2 sound output appear in Windows: Speaker and Digital.
When playing AC 3, my sound card (HF D1B) was configured to use the digital out. Then when playing PCM 5.1, I left it on digital. If to play PCM 5.1, I switch to using the Speaker output, then the volume is similar. 
 
 
Now I have another question: When I play PCM 5.1 or AC3, and in AC3filter I switch off the center channel, there is still some sound coming out of the center channel. I suspect that the HF D1B is applying a Dolby Prologic (or something similar) processing on my sound before outputting it. How stupid is this.... Any idea how to switch that off? 
 
Serge