Search the Community
Showing results for tags 'test disc'.
Found 1 result
Sup y'all. maxmercy was curious about how the OPPO BDP-105 would handle a worst case scenario with 7 channels of re-directed bass added to LFE so he was nice enough to send me a bare bones version of his upcoming test disc project. So I got to play with sine wave tones from 1Hz to 60Hz held to just under 0dB on all channels. From there I had fun experimenting with re-directing each set of channels and viewing the effect on the waveform on an analog scope. Max's upcoming test disc will be a more comprehensive version with many more test tones and sweeps and will hopefully be available sometime this summer. It's going to be a powerful tool and I recommend it to anyone who wants to find out how their system handles re-directed bass so you can avoid sending a clipped signal out to your amplifiers when playing strong bass content. I hooked the subwoofer out of the OPPO to a dummy load in parallel with the scope. The dummy load and the scope's input impedance measured 9.86K. I figured this was kind of a worst case input impedance load too as most amps that I've used were equal to or higher than that. I double checked voltages with my Fluke meter but I'm not going to bother posting the numbers because the scope was in agreement with it for the following pictures. I post the volts per division for the scope's graticule (grid) in some of the following pictures. From there you can find the peak of the waveform and have a good idea what the peak voltage is. Also, for all of the following measurements, sub trim was kept at 0dB. What I found for the OPPO is that it's analog out is even more robust than I was told it was and does not clip in WCS 7.1 channels of full bass even when volume was pushed to a maximum level of 100. It peaked out at a level of ~3.1V with 7ch of re-directed bass at 100MVL. Now for the bad news... when the OPPO adds even 1 WCS channel (center) with the WCS LFE channel, it starts to clip the waveform. The more channels from there that you re-direct to the sub out, the more prominent the clipping becomes and therefore, the more distortion is added to the signal. The OPPO does output a full level LFE by itself very clean however and it is unclear at this point how much additional level it takes from other channels to begin clipping. This clipping has nothing to do however with the analog output IMO. The clipping is present and unchanging no matter what the MVL is set to. It must be reaching some kind of headroom limit on the digital side of things when the signals get summed together. I plan on contacting OPPO's tech department this week and I will keep you guys posted on what the explanation/fix might be. I am disappointed to say the least because I believe that this will affect the hottest peaks of strong bass content and there is no way to compensate with a trim/MVL adjustment. I have more to post about this and other tests and will do so as time permits.