What is Audio Bitrate: Fully Understand Audio Bitrate and Audio Quality
Bitrate is a crucial metric in determining audio quality. In digital audio, various terms such as bitrate, sample rate, bit depth, and dynamic range describe audio data and format. However, their physical meanings and the relationship between these values and the final audio file's sound quality can be confusing and often misunderstood.
Common misconceptions include equating bitrate with bit depth, dynamic range with maximum volume or sound pressure level, and confusion when selecting the appropriate mp3 bitrate (code rate) during audio file conversion. Additionally, there may be misunderstandings when choosing recording or playback device parameters.
In this article, we will explore how bitrate and other numerical metrics impact audio quality, helping you comprehend the relationships and differences between these metrics.
What is Audio Bitrate?
Audio bitrate refers to the amount of data used to represent audio information per unit of time, typically measured in kilobits per second (kbps). It is a crucial parameter in determining the quality of digital audio files, as it directly affects the level of detail and accuracy in the sound reproduction.
There are two primary types of audio bitrate: constant bitrate (CBR) and variable bitrate (VBR):
- Constant Bitrate (CBR): In CBR encoding, the bitrate remains consistent throughout the entire audio file or stream. This means that the same amount of data is used to represent each second of audio, regardless of the complexity of the audio signal. CBR encoding is simpler and easier to manage, as it results in predictable file sizes and bandwidth requirements. However, it may not always provide the most efficient use of data, as some parts of the audio signal may require more or less data to accurately represent the sound.
- Variable Bitrate (VBR): VBR encoding dynamically adjusts the bitrate based on the complexity of the audio signal at any given moment. This means that more data is allocated to complex sections of the audio, while less data is used for simpler parts. VBR encoding can provide better overall audio quality at a smaller file size compared to CBR, as it more efficiently utilizes data. However, it can also result in less predictable file sizes and bandwidth requirements, making it more challenging to manage for streaming applications.
A higher bitrate generally results in better audio quality, as more data is available to represent the original audio signal. Conversely, a lower bitrate may lead to a loss of audio information, resulting in lower sound quality. This is because the audio compression algorithms used in encoding digital audio files remove some of the audio data in order to reduce the file size, especially in lossy formats like MP3 and AAC.
The impact of bitrate on audio quality also depends on the type of compression used. Lossless compression (e.g., FLAC, ALAC) preserves the original audio data, so the sound quality remains high even at lower bitrates. However, lossy compression (e.g., MP3, AAC) discards some audio data to reduce file size, which can result in a noticeable loss of quality at lower bitrates.
What are Factors that Affect Audio Bitrate?
There is a calculation formula regarding bitrate, sample rate, bit depth, and channel:
Audio Bitrate = Sample Rate × Bit Depth × Channel
Sample Rate
Sample rate is defined as the number of continuous signals collected per second by a digital conversion device (such as a sound card or IO) during the process of converting analog signals to digital signals. The unit is Hz. For example, a sample rate of 8 kHz means that there are 8,000 sample points collected per second. This parameter is well-understood by musicians and recording engineers, as formal audio professional books provide clear and unified explanations. The sample rate is an important factor influencing audio bitrate; higher sample rates result in higher bitrates and better audio quality.
However, when searching for information on audio sampling and bitrate calculation, the term "sampling frequency" may appear. For instance, "Sampling audio at 8K frequency, 16-bit depth, file is stereo, find the bitrate of the file" – the first part of this question actually means "the sampling rate of the file is 8 kHz," not "the sampling frequency is 8 kHz."
