OPPO BDP-83 Down-Mix Details

June 28, 2010

Intent

The intent of this test is to experimentally verify how 5.1 LPCM 24bit/48kHz content authored to DVD-Audio is down-mixed to the ANALOG stereo outputs of the BDP-83 Blue-ray player. The DVD-Audio tracks used here have NO EXPLICIT DVD-A down-mix tables specified. The results also display the output levels for each of the multichannel 5.1 outputs for various input tracks. (NOTE: the two Surround Back channels SBL, SBR for a 7.1 system are not measured here).

Testing Configuration

DVD-A content was authored with WaveLab6. Audio content consisted of 24bit/48kHz STEREO and 5.1 tracks with pure sine waves. The default cga 12 was used. In all cases below, the digital amplitude in any PCM channel is either -12 dbFS (1/4 of peak digital amplitude) or zero: Each test result consists of analyzing DVD-A playback audio from TWO output analog channels of the BDP-83.

OPPO BDP-83 with two channel connection at various ANALOG Outputs
BDP-83 output level set at 100%
BDP-83 multichannel analog output speaker settings:
  Downmix  5.1CH  
  FL, FR, C, SL, SR set at LARGE
  Sub ON
  Trim = 0dB (default) for all channels

Sound Card: Creative X-Fi Elite Pro Line-In
Mixer Settings of Audio Creation Mode Console:
  Rec-In at 50%  (0dB)
  96 kHz internal sampling rate
  All input playback levels muted
  EQ, EAX etc. all DISABLED

RMAA 6.2.1 configured at 24bit/96kHz and RECORD ONLY mode.
RMAA displays spectral content and Output dB signal levels for two-channels tested
(N.B. The maximum output level of the BDP-83 is different than the maximum INPUT level of sound card.
This acounts for the (-12 to -10.8) dB differences. Output levels for all cases can be directly compared and
are believed accurate to within 0.1 dB)

GENERAL OBSERVATIONS ON RESULTS

(1) Note that the STEREO test wave used has the same 1 kHz frequency in both channels.

(2) The 5.1 multichannel test waves used have different frequencies in ALL channels 
	(from 1kHz to 6 kHz consecutively for FL, FR, C, Sub, SL, SR)

(3) A STEREO PCM wav file produces exactly the same output signal amplitudes from the STEREO 
    analog outputs and the FL/FR 5.1 analog outputs.

(4a) A 5.1 PCM multichannel wave with audio only in the FL/FR channels produces AT THE 
      SURROUND FL/FR analog outputs the SAME signal amplitude as for the STEREO PCM wav file (3)
(4b) A 5.1 PCM multichannel wave with audio only in the FL/FR channels produces AT THE 
      STEREO analog outputs a ~ -8dB LOWER signal amplitude as compared to the STEREO PCM wav file.
      (This is reasonable as it allows for multichannel headroom down-mix to STEREO output without overload.)

(5) A 5.1 PCM multichannel wave with AUDIO IN ALL CHANNELS produces 
     the expected -10.8dB signal level at all 5.1 surround ouputs EXCEPT FOR THE SUB CHANNEL WHICH IS ~ 5dB LOWER. 

(6) A 5.1 PCM multichannel wave with AUDIO IN ALL CHANNELS produces as expected a down-mixed blend of channels
     to the STEREO analog outputs BUT THE SUB CHANNEL SIGNAL IS EXTREMELY LOW (see spectrum) compared to the
     SUB output in the 5.1 multichannel SUB channel.

Results:

STEREO DVD-A Track both channels 1 kHz:

5.1 DVD-A Track, only FL/FR channels contain nonzero audio:

5.1 DVD-A Track, all channels with audio data: