Dolby Introduces TrueHD 96kHz Upsampling
New audio coding brings sound improvements to Blu-ray audio
This week at the Fidelity Forum—a press event hosted by Dolby—a new system was unveiled that takes Blu-ray audio to the next level.
Higher sampling rates can make a big difference in audio. Simply put, the sampling rate refers to the number of times an audio signal is sampled per unit—in this case we’re talking about the samples per second (Hz). More samples per second generally means a better audio signal. The audio on most Blu-ray discs is sampled at 48kHz. That’s not bad, and we’ve been pretty happy with it for the past couple of years, but more is always better. The trouble is that even the original movie tracks are usually only recorded at 48kHz, so once a movie migrates to disc, there isn’t much that can be done. Dolby’s new system upsamples that audio signal to 96kHz at the master stage prior to the Dolby TrueHD encoding, so you get lossless audio with fewer digital artifacts.
Actually the “fewer digital artifacts” part comes from a feature of Dolby’s upsampling process called de-apodizing which corrects a prevalent digital artifact known as pre-ringing. Pre-ringing is often introduced in the capture and creation process and adds a digital harshness to the audio. The apodizing filter masks the effect of pre-ringing by placing it behind the source tone—the listener can’t hear the pre-ringing because it’s behind the more prevalent original signal. The apodizing filter was adapted from technology developed by Meridian for audiophile-quality CD players selling for $18,000.
I was able to hear the results of the new upsampling process at Dolby’s Fidelity Forum this week at the company’s San Francisco headquarters. During the demonstration, all the samples sounded fuller, more distinctive and with a better soundstage. What was particularly surprising was the effect of the apodizing filter. I was initially skeptical, because the engineering description of pre-ringing seemed more like jargon, but in practice, I could definitely hear the difference. Higher tones seemed less severe and more natural. There also seemed to be improvements in the overall ambiance of soundtracks—an airy quality that made the 48kHz versions seem flat. The results can be subtle, but they’re noticeable enough that if you’re looking for the best audio, it is worth it.
There are already home theater components that include built-in upsampling features, but since the Dolby system hits the signal with upsampling before it’s been encoded to TrueHD, the result is closer to the source. Also, other upsamplers won’t do the apodizing filter trick that contributes a lot to the final results.
In order to enjoy the benefits of a 96kHz disc, you’ll need an AV receiver cable of playing it. Generally, newer receivers can, but not all of them. Many new receivers support sample rates up to 192kHz.
Dolby said several mixing houses have already upgraded their systems to take advantage of the new technology. In the US, two new releases Satchurated: Live in Montreal and San Francisco Symphony at 100 will feature the 96kHz soundtracks. Dolby created a new logo for display on discs that include 96k audio (see the Saturated disc pictured).
Ideally we’d have Blu-ray discs with audio that was recorded natively in 96k, but that rarely happens, especially on film titles. Until that becomes more common, Dolby’s solution is a boon for people who value the sound as much as the picture. It’s also a great tool for the enormous back catalog of movies that have yet to be released on Blu-ray discs, and even more reason to make sure our audio gear is up to date.
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