When it comes to digital audio, a few key terms are important to understand: sample rate, bit depth, and bit rate. These three basics may seem confusing at first. Still, they all play essential roles in determining the audio quality you hear. It’s important to distinguish between the three when recording a podcast, converting a video to audio, or saving a recorded file to share it further on podcast directories, such as Spotify or Apple Podcasts.
This piece will uncover what bit rate, bit depth, and sample rate mean, shed light on their differences and why it’s important to distinguish between them. We’ll also reveal their impact on the audio quality, resolution, and size.
How is sound recorded digitally?
To fully grasp the distinction between sample rate, bit rate, and bit depth, it’s essential to comprehend the exact process of how sound is digitally recorded.
Sound is recorded digitally using a process called analog-to-digital conversion (ADC). This involves converting the continuous analog waveform of sound into a series of discrete digital samples, which can then be stored and manipulated as digital data.
The process of ADC involves the following steps:
- Sampling: The analogue sound wave is sampled at regular intervals to capture its amplitude at each point in time. The rate at which the sound is sampled is called the sample rate, and is usually measured in kilohertz (kHz). The higher the sample rate, the more accurately the sound can be represented.
- Quantisation: The amplitude of each sample is quantized, which means it is rounded off to the nearest value that can be represented by the digital system. The number of bits used for quantisation determines the dynamic range of the recording, or the difference between the loudest and softest sounds that can be captured.
- Encoding: The quantised samples are encoded into a digital format, such as PCM (Pulse Code Modulation), which is the most common format used for digital audio.
Once the sound has been digitised, it can be stored and manipulated in a variety of digital audio formats, such as WAV, MP3, or AAC.
So when someone speaks into a microphone, their voice creates a pressure wave that moves through the air. This wave causes the diaphragm in the microphone's head to vibrate. This vibration, in conjunction with the microphone's transducers, produces an electrical signal that fluctuates in correspondence with the pressure waves. This sound is then converted into a digital signal that can be saved and processed on a computer. The process involves three important factors: sample rate, bit rate, and bit depth.
What is a sample rate?
Sample rate refers to the number of samples of audio that are taken per second. A sample, in turn, is a snapshot of the audio at a specific point in time, and the sample rate determines how often these snapshots are taken. The higher the sample rate, the more accurate the representation of the audio will be. The most commonly used sample rate in music production and podcasting is 44.1kHz, which means that 44,100 samples of audio are taken every second. Some high-end audio equipment and software use sample rates as high as 192kHz, which provide even more accurate representations of the audio.
At what point does the sample rate pop up in the audio recording process, though? The term ‘sample rate’ pertains to the frequency of the wave generated by the sound being recorded.
To have a better understanding, remember the animation technique used in older films that feels like an album pages are flicked through. The rapid movement of these still images gave the illusion of movement, which is frame rate.
The sample rate in audio functions in a similar way to the frame rate in video: The more sound being captured over a short time period, the more precise the sound is reproduced.
The standard sample rate for audio recording is typically 44.1kHz.
What is a bit depth?
Bit depth is another important concept in digital audio. It refers to the number of bits that are used to represent each sample of audio. The more bits that are used, the more accurately the sample can be represented. The most common bit depth used in music production and podcasting is 16-bit to 32-bit, which provides a relatively high level of accuracy. However, some high-end audio equipment and software use 24-bit or even 32-bit bit depths, providing even more accurate audio representations.
But what is a bit, exactly?
The binary values used by computers to store information are commonly known as 'bits.' So when audio signals are sampled, the information is stored in bits. And bit depth implies the amount of this information that can be stored.
In the realm of audio sampling, opting for a 24-bit depth can yield more refined subtleties and precision in comparison to a 16-bit depth. As such, try to consistently record in 24-bit, as it’s currently considered the gold standard for producing super high-quality audio.
When recording your audio at a 24-bit depth, keep in mind that it could result in a larger file size. The decision on which bit depth to choose depends on your intended use of the recording. If you have sufficient storage space and plan to edit the recording, 24-bit is recommended. However, if your goal is to make your content available for streaming, 16-bit may be the more suitable option.
What is a bit rate?
Bit rate is the number of bits used to represent one second of audio. It’s calculated by multiplying the bit depth by the sample rate. For example, a 16-bit audio recording at a 44.1kHz sample rate would have a bit rate of 705,600 bits per second (16 x 44,100).
The bit rate operates in a similar manner to the sample rate, but it measures bits instead of samples. Bit rate measures the bandwidth of data transmission equipment and is expressed in kilobits per second (Kbps), which is equivalent to thousands of bits per second.
When it comes to audio, the bit rate is a term used more commonly for streaming or playback rather than audio recording. Essentially, a higher bit rate means better audio quality because each ‘bit’ captures a piece of data that can reproduce the original sound. So the more bits in a unit of time, the closer you are to recreating the original sound wave that your mic has produced.
However, higher bit rates also mean larger audio files, which can be problematic for editing your show, mixing it, distributing to podcast directories, and storing on your device. For recording, the default bit rate typically falls within the range of 128kbps to 192kbps.
If you choose a bit rate within this range, the audio recording will closely resemble the original.
🔴 Bit rate is the number of bits used to represent one second of audio. A higher bit rate means better audio quality and, thus, a larger file size.
🔴 Bit depth is the number of bits that are used to represent each sample of audio.
🔴 Sample rate is the number of samples of audio that are taken per second. The higher the sample rate, the more accurate the representation of the audio will be. The most commonly used sample rate in music production and podcasting is 44.1kHz.