I’ve mentioned in several of my articles and reviews that I have a bass issue with both my Toshiba HD-A1 HD DVD player and my Sony BDP-S1 Blu-ray Disc player.  I had trouble finding the time to investigate, but I think I now have enough evidence to raise an issue, but before I did, I wanted to be very sure of my observations before I wrote to explain what I found.  Frankly, I’m a bit confused that: a) both players seem to have the same error; and, b) I’m unaware of anyone raising this issue on another site or in another venue.

When I upgraded the Toshiba player’s firmware to a level that would support Dolby TrueHD by decoding the advanced CODEC internally and outputting the 5.1 signals on its analog connectors, I was very enthusiastic.  I immediately made the analog connections to my B&K Reference 30 audio decoder.  I then went through the Toshiba’s setup procedure to set my speaker type to small with a subwoofer, set the crossover frequency to 80 Hz, set the propagation distances between each 5.1 speaker and my ears, and left the 5.1 channel amplitudes at 0 dB.  I pulled a couple of HD DVDs off the shelf that had Dolby TrueHD tracks and auditioned them.  I noticed a delightful improvement in the timbre and accuracy of voices, music, and other sounds, but I was immediately struck by a lack of bass.

I had a similar experience with the Sony BD player.  I set the player to transcode Dolby Digital and DTS tracks to PCM, I set my speakers to small, enabled subwoofer use, and specified the existence of the front center and the surround speakers.  The Sony cannot yet accept user preference for crossover frequency, allow channels levels to be varied, or accept propagation distances (if I missed it, please let me know - I hope that lack of completeness of setup parameters is corrected in the not too distant future).  I auditioned both native PCM tracks and PCM outputs generated by digital audio tracks like DTS HD Master.  And once again I noticed a severe lack of bass energy.

At first I suspected my B&K decoder, the only thing the two signals have in common.  So I checked electrically and acoustically using my Denon DVD-9000 player and the two high definition players as sources.  I played wideband pink noise from not one but two test discs: The AVIA Guide to Home Theater and Digital Video Essentials.  I used my Audio Control SA-3050A third-octave band analyzer to make the measurements.  The disc produced proper bass levels from all three players when the B&K did the decoding of a digital bit stream from the test discs.  But for the HD DVD and BD’s internal decoders, I discovered something quite startling.

It didn’t matter which test disc I used; they both produced the same result.  For a front center channel wideband pink noise test signal, the players’ subwoofer output was approximately 16 dB lower than the center channel output.  16 dB!  The measurement was made at the analog connectors on the back of each player.  The B&K was not in the signal path.  The noise test signal I used was not the band-limited noise used for channel balancing.  The test signal I used was dead nuts flat above the crossover frequency on the center channel output and just as flat below the crossover frequency on the subwoofer channel output.  (It’s the same type of test signal I use to set my parametric equalizers.)  But the amplitudes were very different. 

A subwoofer output at -16 dB is outrageously low.  And although it is possible to increase the subwoofer gain and decrease all the other channels’ gain internal to the B&K, that would force me to crank up the master gain considerably to compensate when listening to an HD disc player’s analog outputs.  If I were to switch to any other source that produced normal levels without first adjusting the master gain, the decoders output would be so high that I’d risk doing damage to my speakers (and ears).  A level difference of 16 dB represents a 6.3:1 amplitude ratio and a power ratio of 39.8:1.  That simply won’t do.

I’m beginning to wonder if comments published elsewhere complaining that the dialog is very low on high definition discs isn’t related to my previous observations in disc reviews that more headroom was left for sound effects on the tracks.  That phenomenon is only 3 to 9 dB, depending on the disc.  Perhaps other users have greatly reduced the static input gain for all analog audio channels but the subwoofer input to achieve proper spectral balance and they were really complaining about having to turn the master gain very high to compensate.

To compensate for the subwoofer channels’ low amplitudes, I fabricated non-inverting op-amp amplifiers to place between my players and the decoder and fine-tuned their gains to achieve amplitude parity between the subwoofer signals and the center channel outputs as measured by my third-octave band analyzer.  But how the hell is a typical consumer going to do that? 

When I played a Blu-ray Disc using the analog audio signals with the externally boosted subwoofer level, the bass was very much improved; it started to resemble what I’ve come to expect from my home theater rig.  But, as I watched and listened to several Blu-ray Discs, I found that I could localize the sound of the subwoofer; it was reproducing the upper bass range.  The Sony player’s crossover frequency is probably higher than 80 Hz.  (I could have measured the frequency with my analyzer, but I was too distracted by the amplitude problem to have notice.)  Fortunately, my M&K subwoofer has an internal, adjustable crossover of its own.  I usually set it to the highest bass frequency and allow my B&K decoder to perform the filtering (something it does not do for analog signals).  Since I could not accept Sony’s upper bass content, I cranked the subwoofer’s crossover frequency down to between 80 and 100 Hz and the offending upper bass went away.  I may have been left with a small depression in the flatness of the upper bass, but acoustical measurements reveal that it seems to be very minor.

I managed to solve the problem, but this was a problem that shouldn’t exist.  I notified both Toshiba and Sony and their engineering people are trying to reproduce the problem on the test bench.  When and if they get back to me, I’ll be glad to pass the information along to you. 

But, there’s always the possibility that I’m simply having a serious cockpit problem.  So I’d be very curious to hear from readers who are using these particular players’ internal decoders.  I’d like to understand your impressions of discs’ bass content, particularly from those who own subwoofers.  If you believe you’ve established normal frequency balance, I’d be curious to know how.  And if I’ve somehow missed something very fundamental in the operation of either player or both, please write to explain the error of my ways.  I can be reached at dan at dvdfile dot com (you know what to do with that address).

I’m utterly baffled that either no one else has noticed this problem or that I just happened to have two players of two different formats designed and manufactured by two different companies, and each has the same flaw.  Of course, the other explanation is that home theater obsession causes madness and I’m now officially bonkers.