Tag Archives: cd

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

We went to see Andy McKee last night and talk about dynamics!!

Unlocking dynamics

Dynamic range describes the difference between soft and loud. What’s not defined is how soft or how loud—only the magnitude between the two—which is a problem if the softest sounds fall below the threshold of audibility. When that happens the range of dynamics is truncated, a fact not apparent when quoting dynamic range figures.

I’ll give you an example. The threshold for hearing is defined as the minimum amplitude the average person can detect sound. This level happens to be around 15dB for a middle-aged male. If we want to be able to listen to the full range of a CD, which is 96dB, we have to adjust the system’s loudest peaks to be 111dB (15dB + 96dB). That’s pretty loud and beyond the capability of most speakers to comfortably hit those levels. Which means we aren’t going to get the full dynamic range possible out of a CD.

But, wait a minute. A CD is 16 bits limited in dynamics (96dB). Higher bit depth, like 24 bits, can theoretically go as high as 144dB, though noise and other factors set the practical limit at about 123dB. How then can this greater dynamic range from greater bit depth matter, if we’re already losing dynamic range to the threshold of audibility?

It can’t, at least not by much.

And vinyl? Heck, we’re lucky to get 70dB from well-pressed vinyl, forcing the mastering engineer to compress the presentation into that smaller space. That said, vinyl’s the only medium that actually scales pretty easily. You get it all at most volume levels, though the price is the compression.

So, the bottom line in this ramble is simple. Even though a CD is limited to 96dB of dynamic range, by making sure to turn the level up so the softest passages can just pass the threshold of audibility, we can get close to the dynamics of live music. Deeper bit depth makes it easier, but not by a lot.

 

Asheville, Walnut Cove, Biltmore Forrest and Western North Carolina’s Audio and Home Theater specialists present Cane Creek AV and Paul McGowan – PS Audio, Intl.

Getting something for nothing

We all like the idea of getting something without having to pay a penalty: that free sample at the market, a kind gesture, a door being opened when your arms are full. Closer to home, more digital audio information than we started with.

When we upsample a 44.1kHz 16-bit file to a higher rate and depth, like 96kHz 24 bits, we typically get better sound quality. And since the magic of upsampling just sort of works at the touch of a button, we seem to be getting more for nothing. After all, the file size is considerably bigger. There must be more there. Right?

So, how does that work? How can a program know what went missing from the original recording so it can add it back in?

There are actually two things going on. The first, and least important, is interpolation. Interpolation is a mathematical process that adds more data points through intelligent guesswork and statistical analysis. Simply put, if our steps are moving in a predictable pattern: 1, 3, 5, 7 then it’s likely we can add the missing steps: 2, 4, and 6, as additional data points so we wind up with 1,2,3,4,5,6,7.

Perhaps more important is the choice of filters. With standard CD rates of 44.1kHz we need to have a fairly steep filter so we don’t run into trouble above 22kHz. By increasing to 96kHz we can apply a much gentler and better sounding filter to our digital data and this, in my experience, is responsible for the majority of what we might consider better sound from upsampling.