16 vs 24 bit

Discussion of the mysteries behind bit-depth, sample rates and sound quality

It's just designed to get the new person up to speed on the issues and provide a strong sense of perspective on what really matters. We are going to talk about bit depth and sample rates, how these translate into storage requirements, and then talk about the subjective differences between the two methods of recording your music. In short, what is the relation of 24 bit recordings to the "sound quality" we all want.

Never refer to 16-bit or 24 bit audio as the "bit rate". Its properly called the bit depth and the pros will be so irked they'll have to correct you.

A few years ago the world of digital audio was much simpler. Products that recorded and generated digital audio were all 16 bit. Compact discs, the main method for music distribution, has digital audio that has a bit depth of 16 bits and a sample rate of 44.1 kHz.

Gradually, products began to appear with a higher bit depth - an 18 bit drum machine, 20, then 24 bit effects processors. Then recorders made the leap to 24 bit. Today, your audio interface is probably 24 bit and allows you to select sample rate of your choice, 44.1, 48, 88.2, 96 and even 192khz. Multi track recorders vary between 16/44.1 and 24/96. When you buy one you have to decide which way to go and get it right the first time.

So what do all these number mean and how important are they? That's where we are going to go. First, you have to have these definitions under control.

Bit Depth refers to the number of bits you have to capture audio. The easiest way to envision this is as a series of levels, that audio energy can be sliced at any given moment in time. With 16 bit audio, there are 65, 536 possible levels. With every bit of greater resolution, the number of levels double. By the time we get to 24 bit, we actually have 16,777,216 levels. Remember we are talking about a slice of audio frozen in a single moment of time.

Now lets add our friend Time into the picture. That's where we get into the Sample Rate.

The sample rate is the number of times your audio is measured (sampled) per second. So at the red book standard for CDs, the sample rate is 44.1 kHz or 44,100 slices every second. So what is the 96khz sample rate? You guessed it. It's 96,000 slices of audio sampled each second.

So lets put it all together now. This brings us to the Bit Rate, or how much data per second is required to transmit the file, which can then be translated into how big the file is. Your CD is 16bit, 44.1 so that is 44,100 slices, each having 65,536 levels. A new Audio interface may record 96,000 slices a second at nearly 17 million levels for every slice. If you think that is a lot of data, well, you are right, it certainly is. The Bit Rate is usually expressed in Mbit/sec. But you don't need to do all this math. I'm going to do it for you. This is not an important area in the recording process to get sidetracked on. What is important for you is how this translates to your hard drive storage.

A 44.1 kHz/16-bit recording uses 5.2 MB a minute per track. A 48 kHz/24-bit recording uses 8 MB a minute per track. File sizes are twice as large at 96 kHz/24-bit, up to 16 MB a minute.

So you see how recording at 24/96 more than triples your file size.

So you should be noting two things now: 1. Recording at 24/96 yields greatly increased audio resolution-over 250 times that at 16/44.1 2. Recording at 24/96 takes up roughly 6 times the space than recording at 16/44.1