How Digital Recorders Work - The Basics

How Digital Recorders Work - The Basics

Last Updated on October 19, 2017

How Digital Recorders Work - The BasicsDigital recorders are amazing inventions that let us capture exact sounds from the past and replay them for as long as we want.

This technology has allowed humanity to do some absolutely amazing things – no doubt about it.

But have you ever wondered how voice, call and sound recordings work?

It’s a fascinating process … so let’s begin.

The Nature of Sound

In order to record sound, we first need to understand it. So, what exactly is sound?

When we hear a sound, we’re really “hearing” tiny changes in air pressure.

When an object vibrates, it displaces the air molecules next to it. These molecules then displace additional air molecules, causing a chain reaction.

This creates a “front” which moves through space, for a set distance, depending on the strength of the original vibration.

Our ears are finely tuned to pick up on these “fronts”, and interpret them as sound in our experience.

The Nature of Recording

So, that was a quick overview of what sound is. There’s a lot more complexity obviously, but that gives you enough to move forward.

It’s one thing to know how sound works. It’s an entirely different thing to understand how to capture that sound and be able to play it back at any time.

Here’s the thing about recordings: both audio and video are both illusions.

Meaning, when we see a recorded video, or listen to recorded audio, we’re not getting a TRUE recording of the past.


Because the way recording works, both audio and video, is by recording snapshots of the moment.

Take a movie for example. A video camera will take extremely fast snapshots of a moment in time… say, 30 shots per second.

Then, when those shots are played back at the same rate, they all connect together, and it’s impossible to tell that they’re actually just individual shots.

The same is true with audio.

With recording devices, you’re getting individual snapshots of every split second moment possible. When those snapshots are strung together at the same rate they occurred in real time, you get the recording.

This is also how we can easily speed up and slow down recordings, and manipulate them in all kinds of different ways as well.

How Microphones Work

So, a digital recording is comprised of snapshots, or samples of sound.

But how do you get the samples? Microphones.

Sound waves distort the air around them. But in order for them to be recorded, they need to be changed into another type of energy.

This is why the microphone exists – to transduce, or change the energy type of the sound wave, from a change in air pressure, to a change in electrical voltage.

The microphone gives us the same samples of air pressure, in electronic form, which is something we can work with and store.

When the microphone picks up sound, it’s in analog format. So, once the sound is recorded, it will go through an ADC, or, analog-to-digital converter.

The ADC will also give each sample its own unique number id, which will be stored on the recorder’s storage device.

How Audio is Stored

The ADC can both write numbers and read them. When it receives sound, it will provide its own unique number. To the ADC, that number represents the exact amount of voltage required for each individual sample of sound.

When the sound is played back, it passes through an amplifier, which takes the voltage amount and turns it back into a change in air pressure, allowing us to hear it.

How Many Samples Make a Sound?

Earlier in this article, we talked about how video and audio recording is similar.

However, for audio recording to work, we need a LOT more samples than we’d need snapshots of a video.

Where many movies and videos play at around 60 frames per second (FPS), we need thousands of more samples for every second of audio.

The amount of samples required, depends on the frequency of the sound being recorded. If you want to record a sound at the frequency of 8,000, you’d need to take at least 16,000 samples.

Thoughts on the Process

This, in a very small nutshell, is the digital recording process. As you can see, digital recording is not just one invention in and of itself.

It’s an entire process that works together, to give us the recording capabilities we have in this day and age.

By turning changes in air pressure into electricity and storing it digitally, we gain the ability to mold and manipulate that data however we see fit.

We can change pitches. We can increase or decrease the volume. We can delete entire sections. We can change which audio gets played when.

This is what allows our call recording technology to function. Using this exact process, we can store over one hundred thousand hours of calls on a single hard drive.

Next time you hear a sound, think about what had to happen for it to get to your ears.

And next time you hear a recording, think about how the sound was turned into electric voltage, stored, then recalled, and turned back into air pressure, just so you can hear it.

Last Updated on October 19, 2017