I'm measuring the Center channel of a soundbar that's composed of 3 drivers. I'm using a sound mode that doesn't upmix to other channels, and the sub is disconnected. I'm measuring all within a single REW session, and the UMIK-1 remains in the same position throughout. I'm using 48 kHz sweeps all output through the same HDMI port on the laptop, with timing reference always on the Center channel. I measure using the REW-generated sweep using ASIO4ALL (7.1 channels), as well as file playback in various formats produced by taking the REW-produced sweep file and encoding it as the center channel, with silence on all other channels. The file formats measured are 7.1 LPCM, DD 5.1, DTS 5.1, DD+ 5.1, and DD+ 9.1.6 (the Dolby ones are bitstream output over HDMI). When I look at the Delay that REW notes for each measurement, it's pretty much all over the place. For example, 3 sweeps with ASIO4ALL, the Delays are 0.0288, 0.1385, -0.0001; the corresponding Clock adjustments are 0.3, 117.4, 1.2. With a 7.1 LPCM file, example Delays are -0.0031, 0.0429, -0.5497; the corresponding Clock adjustments are 1.4, -1.1, 2.4. With DD 5.1, example Delays are 0.0016, -0.0656, -0.2180; the corresponding Clock adjustments are 33.3, -6.9, 7.8. If look at some DD+ sweeps where no clock adjustment is reported (some do have clock adjustment), the Delay is fairly consistent, but non-zero: 0.0235 to 0.0252.
What's the likely explanation for this variability?
What's the likely explanation for this variability?