Hi everyone,
I am seeking help from the audio engineers here to understand a frustrating leveling issue involving DUDU7 Android head unit acting as a digital transport for my car's Helix DSP.
I use Poweramp configured in Hi-Res Output / Follow Track Mode with all internal DSP turned off. It outputs via USB to an SMSL PO100, which sends an SPDIF optical line to my DSP. The hardware lights up correctly (Green for 44.1kHz, Blue for 96kHz), confirming no resample is taking place. Despite this "bit-perfect transport" behavior, I am noticing a mandatory -3dB drop whenever I play a true Mono file (0dBFS 40Hz test tone A), whereas an identical Stereo file (Tone B) plays at a perfect 0dBFS.
I have isolated this to the Android system mixer's downmixing/panning law matrix. Because my specific head unit firmware doesn't allow applications to lock into USB Exclusive Mode, the OS forces a mono-to-stereo channel duplication and drops the volume to prevent digital clipping. Hiby Player fixes this because it uses an independent USB driver, but I prefer Poweramp's interface for daily use. Hiby player output 0dbFS on 40hz 0db tone even if I'm using RCA or SPDIF directly from head unit.
If I turn on Direct Volume Control (DVC) and disable Float32, the -3dB drop goes away on the Mono file, but my 24-bit tracks get truncated to 16-bit. I tried this when using Optical directly from head unit, while in current USD audio mode, no option to disable float32 I think.
How can this Android audio pathway be optimized to treat Mono files with a 1:1 gain structure over a digital stereo link without sacrificing 24-bit high-resolution output? Are there underlying system commands or custom player configurations I am missing?
I feel like the bass response isn't comparable to like same Poweramp player on phone > SMSL PO100 > Optical to DSP. Phone as source has better perception of bass, everything else sounds the same.
Below is the comparison of both tones. Looking forward to your thoughts!
I am seeking help from the audio engineers here to understand a frustrating leveling issue involving DUDU7 Android head unit acting as a digital transport for my car's Helix DSP.
I use Poweramp configured in Hi-Res Output / Follow Track Mode with all internal DSP turned off. It outputs via USB to an SMSL PO100, which sends an SPDIF optical line to my DSP. The hardware lights up correctly (Green for 44.1kHz, Blue for 96kHz), confirming no resample is taking place. Despite this "bit-perfect transport" behavior, I am noticing a mandatory -3dB drop whenever I play a true Mono file (0dBFS 40Hz test tone A), whereas an identical Stereo file (Tone B) plays at a perfect 0dBFS.
I have isolated this to the Android system mixer's downmixing/panning law matrix. Because my specific head unit firmware doesn't allow applications to lock into USB Exclusive Mode, the OS forces a mono-to-stereo channel duplication and drops the volume to prevent digital clipping. Hiby Player fixes this because it uses an independent USB driver, but I prefer Poweramp's interface for daily use. Hiby player output 0dbFS on 40hz 0db tone even if I'm using RCA or SPDIF directly from head unit.
If I turn on Direct Volume Control (DVC) and disable Float32, the -3dB drop goes away on the Mono file, but my 24-bit tracks get truncated to 16-bit. I tried this when using Optical directly from head unit, while in current USD audio mode, no option to disable float32 I think.
How can this Android audio pathway be optimized to treat Mono files with a 1:1 gain structure over a digital stereo link without sacrificing 24-bit high-resolution output? Are there underlying system commands or custom player configurations I am missing?
I feel like the bass response isn't comparable to like same Poweramp player on phone > SMSL PO100 > Optical to DSP. Phone as source has better perception of bass, everything else sounds the same.
Below is the comparison of both tones. Looking forward to your thoughts!
