Digital Audio and Acoustics in Logic Pro X

By Graham English

So what’s the big difference between digital and analog audio anyway? In analog recording, a representation (an analog) of the sound source is reproduced on a physical medium, such as records or tape. In digital recording, multiple measurements are taken of the sound source and stored digitally as binary code, or 1s and 0s. The process of measuring and recording digital audio is called sampling.

The sample rate is how often a slice of audio is turned into a digit each second. The higher the sample rate, the higher the audio fidelity. You want high-quality audio even if your goal is to mangle and distort it. The noise you introduce into your audio should be a choice, not the result of a misunderstanding.

You also want a wide dynamic range, which is the ratio of loudest to quietest sound. Dynamic range is measured in decibels, or dB. CDs have a dynamic range of about 90 dB. Logic Pro is capable of 24-bit recording and has a dynamic range of around 125 dB. You’ll be pleased that Logic Pro is capable of recording audio at and exceeding industry standards, depending on your hardware capabilities.

Ready to get out your calculus textbooks and start plotting sine waves? You’re not? Phew. But it’s important to define some audio terms so you understand the choices you make as you record digital audio.

After you understand some basic acoustic theory, you’ll be able to identify how the choices you make in Logic Pro affect what you hear. Without getting too technical and long-winded, here are some aspects of sound:

  • Frequency is the number of cycles completed by a sound wave in one second. Frequency is measured in Hertz (Hz).

  • Wavelength is the distance traveled over one cycle of a sound wave.

  • Period is the duration of a sound wave cycle in time and is inversely proportional to frequency. The lower the frequency, the longer the period.


Here’s why understanding some audio fundamentals is important. Audio has to travel through the atmosphere to get to you so you can perceive it. A low E string on a bass guitar has a frequency of 41.2 Hz and takes about 27 feet to complete a full cycle. Bass frequencies travel far, so you can hear the low boom of a loud car stereo coming a mile away.

But bass doesn’t always sound good in a small space because it can’t complete a full wavelength without hitting a wall and bouncing around the room. And before you know it, all those bass frequencies pile on each other and multiply, causing room modes. Room modes are frequencies that can be too loud or too quiet based on how sound reacts to the room’s dimensions.

Knowing a little bit about audio will enable you to make adjustments to your sound to improve its quality. Knowing what frequency is and that every sound is made up of multiple frequencies will help you as you record and mix your audio.