What Is Bitrate in Audio?
Bitrate refers to the amount of data transferred per second in a digital audio file. It directly correlates to the quality and size of the audio file. Generally, a higher bitrate indicates a larger file size and higher audio quality because more data is being used to represent the audio information. Bitrate is commonly measured in kilobits per second (kbps).
For digital audio, bitrate specifically refers to the number of bits (or binary digits – 1s and 0s) encoded on the audio file per second. More bits allows more information to be stored and reproduced in the audio. A higher bitrate enables more precise replication of the original analog sound wave’s amplitude and frequency.
Bitrate serves as an important factor in determining the overall audio quality. Higher bitrates allow for lower noise, greater dynamic range, more precise rendering of tones, and a fuller, richer sound. However, higher bitrates also require more storage space. The ideal bitrate depends on the particular audio content and playback scenario.
Measuring Bitrate
Bitrate is a measurement of the amount of data that is encoded to represent a specific audio recording or file. It refers to the number of bits per second (bps) or kilobits per second (kbps) required to encode the audio.
Some typical bitrate ranges are:
- 128-192 kbps – Minimum bitrate for acceptable quality MP3 files
- 192-256 kbps – Good quality MP3 encoding
- 320 kbps – Highest quality MP3
- 500-1000 kbps – Standard bitrate range for lossless CD quality audio
- 1500-3000 kbps – High-resolution lossless audio
Bitrate can be variable (VBR) or constant (CBR). VBR files vary the bitrate dynamically based on the complexity of the audio. This allows for smaller file sizes by using fewer bits during simple passages. CBR files use a constant bitrate throughout. CBR can be easier to stream and edit, but VBR provides better overall quality for a given file size.
Higher bitrates allow more accurate encoding of the source audio but result in larger file sizes. Lower bitrates reduce file sizes but may introduce audible compression artifacts. The ideal bitrate balances audio fidelity with file size.
Bitrate and File Size
There is a direct relationship between bitrate and file size. Higher bitrate = larger files, and vice versa. Bitrate is measured in kilobits per second (kbps), and refers to how much data is being encoded every second in a file. A higher bitrate encodes more data per second, resulting in larger file sizes.
If you take two video files with identical length, resolution, frame rate and codecs – the only difference being the bitrate, the file with the higher bitrate will have a larger file size. This is because it has more data packed into every second of video.
Many factors determine optimal bitrates, but in general higher resolution and higher quality video requires higher bitrates to look good. For example, a 1 hour long 1080p video encoded at 5 Mbps will be around 2.7 GB. The same video encoded at a lower 2 Mbps bitrate would be around 1.1 GB. Cutting the bitrate in half reduces file size by the same amount. The tradeoff is potentially lower video quality at lower bitrates.
Similarly, with audio, higher bitrates lead to better quality but larger file sizes. An MP3 encoded at 320 kbps will sound better than one encoded at 128 kbps, but its file size will be significantly larger as a result.
When encoding media, it’s important to balance desired quality vs. acceptable file size for distribution. But in general, higher bitrate equals larger file sizes.
Bitrate and Audio Quality
The bitrate has a direct impact on the audio quality. Generally speaking, a higher bitrate translates to better audio quality because more bits are used to represent the audio data. This allows for a more accurate reproduction of the original sound when played back. According to https://www.gumlet.com/learn/audio-bitrate/, higher bitrate provides “increased dynamic range, more definition (allowing you to hear each individual instrument), better clarity.”
However, the increase in quality diminishes at very high bitrates. There are limits to human hearing so extremely high bitrates may not translate into perceptibly better quality. As https://blog.discmakers.com/2023/07/what-is-bitrate-in-audio/ explains, “There is a point of diminishing returns, where higher bitrates don’t necessarily mean better quality.” Going above 320 kbps for compressed formats like MP3 may not make an audible difference.
Recommended Bitrates
The recommended audio bitrate depends on the intended use and distribution method. Here are some general guidelines:
For streaming audio, a bitrate of 128 kbps is considered decent quality, while 256 kbps is high quality. Live streaming requires a lower bitrate compared to on-demand streaming due to bandwidth limitations. According to Dacast, 64 kbps is recommended for 360p video, 128 kbps for 480p and 720p, and 256 kbps for 1080p video streaming.1
For mp3 audio files, 128-320 kbps is considered high quality. At 128 kbps, the audio will be clear for most applications. At 192 kbps and higher, the audio is indistinguishable from the original source for most listeners.2
For podcasts, a bitrate of 128 kbps provides a good balance of quality and file size. For heavily voice-based shows, even 64 kbps can work well.3
For lossless audio like WAV files, the bitrate is much higher to preserve full quality. CD-quality audio has a bitrate of 1411 kbps while high-resolution formats can reach 6000 kbps or higher.
When bandwidth is limited, opt for lower bitrates. The minimum viable bitrate depends on the audio content – simpler audio like podcasts need less than music recordings.
Bitrate Encoding
One important consideration when encoding audio is whether to use constant bitrate (CBR) or variable bitrate (VBR) encoding. With CBR encoding, the bitrate stays the same throughout the entire audio file. This results in consistent file sizes and makes streaming easier, but some parts may be encoded at a higher quality than necessary while other parts are lower quality (Variable bitrate – Wikipedia).
VBR encoding varies the bitrate dynamically based on the complexity of the audio. More complex sections use a higher bitrate while simpler sections use a lower bitrate. This allows for smaller file sizes by optimizing quality, but can cause inconsistencies when streaming (IBM: Internet connection and recommended encoding settings).
Many popular encoders today like MP3, AAC, and WMA support VBR encoding. When using VBR, you set a target bitrate and the encoder optimizes to stay near that rate. VBR can produce better quality than CBR at the same target bitrate, but quality can vary from section to section.
Different encoders at the same target bitrate can also produce different levels of quality and efficiency. More advanced encoders like Opus tend to achieve better quality per bitrate compared to older encoders like MP3 (Wowza: CBR vs VBR). It’s important to test different encoder settings to find the optimal balance of quality and file size.
Bitrate for Streaming
When streaming audio content online, there is a balance between audio quality and bandwidth usage. Higher bitrate audio files take up more bandwidth but offer better quality. However, a bitrate that is too high can cause buffering issues for listeners with slower internet connections.
A common technique used in streaming is called adaptive bitrate streaming. With this method, the audio is encoded at multiple bitrates. The player will automatically adjust to the optimal bitrate based on the listener’s connection speed to minimize buffering. Many streaming platforms recommend encoding at 64 kbps, 128 kbps and 192 kbps to provide options for different connections.
For most streaming applications, a bitrate of 128 kbps offers a good balance between quality and bandwidth usage for stereo audio. This provides near CD-quality audio while keeping file sizes reasonable. For talk-based content like podcasts, even 64 kbps can provide good results. However for classical music and other genres where high fidelity is important, 192 kbps or higher may be preferable.
The exact optimal bitrate depends on the audio content itself. More complex audio like classical music requires a higher bitrate than simpler audio like speech. When setting up streaming, it’s recommended to test different bitrates to find the best fit for your particular audio content and target audience.
Bitrate for Podcasts
For podcasts, balancing audio quality and file size is crucial. Most podcasters aim for a bitrate between 48-128 kbps. According to The Podcast Host, the vast majority of podcasts can use 96 kbps mono as this provides good quality for voice while keeping file sizes manageable. They recommend 48 kbps mono as the absolute minimum for spoken word podcasts.
Higher bitrates like 128 kbps stereo may be preferable for podcasts featuring music or high production value. However, this comes at the cost of larger file sizes. As noted by Simplecast, doubling the bitrate from 64 kbps to 128 kbps results in double the file size with only a minor increase in perceptible quality for most listeners.
When choosing a podcast bitrate, it’s helpful to consider the listening environment. Many podcast listeners stream audio on mobile devices or in noisy environments where extremely high audio quality is less critical.
Bitrate for Lossless Audio
Lossless audio formats like FLAC and ALAC provide CD-quality audio in compressed files by removing redundant data. However, uncompressed formats like WAV and AIFF contain raw PCM audio data and have much higher bitrates.
Uncompressed WAV and AIFF files have bitrates of 1,411 kbps, which is over 4 times higher than a typical 320 kbps MP3 [1]. This extremely high bitrate preserves every detail of the original studio recording.
Such high bitrates are best suited for critical listening applications where quality is paramount, such as audio engineering and mixing. The large file sizes make uncompressed lossless impractical for everyday portable use. For typical listening, compressed lossless provides indistinguishable quality at lower bitrates.
Conclusion
Bitrate refers to the amount of information in a digital audio file per second of playback. Higher bitrates offer the potential for higher sound quality, but also result in substantially larger file sizes and bandwidth requirements. The optimal bitrate depends on the type of content and delivery method.
When encoding audio, a balance needs to be struck between quality and file size. Low bitrates can negatively impact quality by introducing audible artifacts and distortions, but bitrates that are too high may be impractical for distribution or unnecessary for certain audio. 128-256 kbps are typical for MP3s and streaming, while lossless formats require 700-5000+ kbps. Higher bitrates are advisable for complex music content, while lower bitrates may be sufficient for simpler podcasts and audiobooks.
Bitrate has a major influence on audio encoding, storage, delivery and playback. Understanding its role allows audio creators and engineers to make informed choices, improve efficiency, manage costs, and ensure the best possible listener experience.
