DVD Vs CD: Which Has Better Audio Quality (And Why)?

CDs and DVDs are the same size, made of the same plastic, and read similarly by lasers, too. However, only one of them — CDs — was built with music in mind. But whether that means better quality is a different question altogether.

Working out which one sounds better starts with how digital audio is made. Digital audio works by measuring sound and its properties thousands of times each second. As that happens, two things determine how good the final output sounds: how often the measurements are run, and how precise each one is. Here, CD is a highly dependable format offering great consistency — every audio CD ever pressed has exactly the same sound because it uses identical settings. It takes 44,100 measurements a second and stores each with 16 bits of precision. These numbers were actually fixed way back in 1980 by Philips and Sony.

DVDs work differently, though, since they are actually more of a flexible container. That means the sound quality is left to whoever makes the disc, and theoretically, the bar is much higher. DVDs permit up to 96,000 measurements per second in stereo, each stored with 24-bit precision. There was even a special music-only version of DVD called DVD-Audio, released in 1999, which took things way up to 192,000 measurements per second. It wasn't popular at all, though, leaving it among several formats that tried to be the next audio CD and never made it.

The trouble with DVDs, though, is that they're mostly used for movies. And most movie releases support Dolby Digital, which is actually a lossy surround sound format from Dolby Laboratories. Lossy means the encoder permanently deletes whatever it calculates your ears will never miss.

Even so, if you take one audio file at the highest quality a studio can possibly produce and write it to a CD, it will have to throw away everything beyond its 44,100 measurements and 16 bits. The DVD should be able to store it without being altered.

However, whether you'd actually be able to discern those differences is a different question. The thing is, a CD's 44,100 measurements-per-second figure wasn't a cost-cutting measure or anything. Rather, it follows a rule called the Nyquist theorem, which states that the measurement rate has to be at least double the highest frequency you want to capture. And since human hearing tops out near 20,000 Hz, going by the theorem, the measurements would have to be set at 40,000 Hz. The CD's rate already clears that with room to spare. So for the DVD, all that additional headroom simply increases the size of the audio file without capturing any additional notes an audiophile would be able to discern.

The extra precision — the bits — also hit a similar kind of ceiling. A CD's 16 bits stretch 96 decibels between the faintest sound it can store and the loudest. That's a pretty wide range, more so than required, since real records come nowhere near using the whole range. Even a superbly engineered classical recording tends to span about 60 decibels from its softest passage to its biggest. But your average pop song most people listen to is often compressed to just 15 decibels. CDs once again offer more than is needed, so DVDs' 24-bit capacity is more than any album would ever need.

Indeed, people asked to spot the difference between the two in controlled tests were unable to do so. One test was performed by Brad Meyer and David Moran of the Boston Audio Society in 2007. They used DVD-Audio and SACD discs, both high-resolution music formats, for firing audio off a high-end stereo – except for half the listening, they routed the same signal through a CD recorder on its way to the speakers. This effectively stripped half of the audio down to what a CD can hold. Listeners were able to correctly pick 49.82 percent of the time, which is coin-flip levels of chance, proving they were just guessing through it all. Of course, a lot of the principles discussed here carry over to the vinyl records versus CD audio quality debate as well.