Phase problems probed; upsampling audio.
QI can’t seem to get clear dialogue when playing some movies and TV shows and am forced to used closed captioning. I believe my problem is caused by improper phase. My home theater setup consists of five speakers plus dual subwoofers that have a polarity switch and phase knob. I’ve heard that the proper way to adjust phase is to play a sine wave at 80 Hz (same as my crossover setting) and then turn off all speakers except the left or right speaker and its adjacent sub. The next step: adjust polarity and phase until you measure the highest SPL level at the main listening position. Am I going about things right? Any other suggestions to improve dialogue intelligibility in my system? AMIT ALCALAY / VIA EMAIL A It’s unlikely that phase problems are affecting dialogue intelligibility in your system. First, the polarity/phase adjustments you describe are intended to minimize frequency response dips in the region where the main left/right speaker output blends with the subwoofer’s output (80 Hz, in your case). Second, the frequency range of movie dialogue rarely extends down to 80 Hz— even if the actor delivering it happens to be Ving Rhames ( Mission: Impossible, Pulp Fiction, etc.)— so the output of your subwoofers shouldn’t affect dialogue clarity.
Where a phase issue could create problems is if the speakers are wired incorrectly. A basic system check would confirm polarity by verifying that all speakers are wired with the positive (red) output on the amplifier connected to the positive input on the speaker, and the negative (black) output connected to the speaker’s negative input.
You could then use a test disc like Disney’s WOW (available from Amazon.com) or any Blu-ray or DVD with the THX Optimizer (I use Pixar’s Toy Story) to check for proper phase between the various speaker pairs in your system. For example, to evaluate phase with your main left and center speakers, in-phase pink noise is played, followed by out-ofphase pink noise. The first tone should sound clear and focused, the second diffuse. If the results you hear are reversed, then one speaker in the pair is wired incorrectly.
Another factor that can reduce dialogue intelligibility is center-channel level. Even when the center speaker’s output is calibrated to match other speakers in your system, the soundtrack and sound effects in some movies can obscure dialogue when listening at a reasonable level. To fix this, you should temporarily boost center speaker level for certain content. Another option if your receiver provides it is to use a dynamic range compression mode such as Audyssey’s Dynamic EQ/ Dynamic Volume or THX Loudness Plus that works to maintain a consistent level among all surround channels at various volume settings. Q When researching DACS, I ran across the Cambridge Audio CXN, a network audio player that upsamples all inputs to a 24-bit/384khz hi-res format using “polynomial curve fitting interpolation.” This seems to be the only DAC that offers that kind of feature. Most Ultra HDTVS and Blu-ray players also provide upscaling, but for video. In my experience, this is a very effective feature that improves the experience of watching a regular DVD. Here’s my question: Does audio upsampling have the same effect as video upscaling? MIKE YANG / VIA EMAIL A Many audio DACS perform some type of upsampling or oversampling before converting the digital bitstream to analog format. According to Cambridge Audio, what’s different about the upsampling technology used in its CXN is that an algorithm interpolates audio data with greater precision than standard sample-rate convertors can deliver, creating
a curved waveform that more closely approximates the original analog audio signal. Other benefits it cites for the CXN include a reduction in jitter distortion and an ability to apply processing to all inputs, including compressed streamed sources like Spotify.
Audio upsampling is in many ways similar to the scaling that happens with Ultra HDTVS and Blu-ray players. For video, however, the processing generates new image pixels instead of converting audio samples.
With most high-quality video scaling solutions, an algorithm scales the original image data using a combination of noise reduction, pixel interpolation (to render smooth, jaggy-free edges), and fine contrast and detail enhancement. As you’ve confirmed with your own eyes, the results can look very good. On the audio side, products like Cary Audio’s AIOS, an upsampling integrated amplifier/dac that delivered impressive performance when Sound & Vision tested it in 2017 (see soundandvision.com), confirm that audio upscaling can also have a beneficial effect.