Tag: compressed audio vs pcm

Audio compression, how it works


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Audio compression, how it works

Audio compression
Audio compression

audio compression

 

audio compression
audio compression

 

Audio compression technology refers to the application of suitable digital signal processing technology to the original digital audio signal stream (PCM encoding), without losing the amount of useful information, or under the condition that the loss introduced be insignificant, reduce (compress) its code rate, and also called compression encoding.

It must have a corresponding inverse transform, called decompression or decoding. The audio signal can introduce a lot of noise and some distortion after passing through a codec system

Audio compression technology refers to the application of suitable digital signal processing technology to the original digital audio signal stream (PCM encoding), without losing the amount of useful information, or under the condition that the loss introduced insignificant, reducing (compressing) its code rate, and also called compression encoding. It must have a corresponding inverse transform, called decompression or decoding. Audio signals can introduce a great deal of noise and some distortion after passing through a codec system. The advantages of digital signal are obvious, but it also has its own corresponding disadvantages, ie increased storage capacity requirements and increased channel capacity requirements during transmission. Taking a CD as an example, the sampling frequency is 44.1KHz and the quantization precision is 16 bits, so a stereo audio signal for 1 minute needs to occupy about 10M bytes of storage capacity, that is, the capacity of a CD turntable is only about 1 hour. Of course, the problem is even more pronounced in the world of much higher bandwidth digital video. Are all these bits necessary? The study found that there is a large redundancy in the direct use of the PCM code stream for storage and transmission. In fact, sound can be compressed at least 4:1 under lossless conditions, that is, only 25% of the digital amount is used to retain all the information, and the compression ratio in the video field can even reach to several hundred times. Therefore, in order to use limited resources, compression technology has received much attention since its inception. The research and application of audio compression technology has a long history, like A-law coding, u-law is a simple almost instant compression technology, and has been applied in ISDN voice transmission. Research on speech signals has been developed before and has matured, and has been widely used, such as adaptive differential PCM (ADPCM), linear predictive coding (LPC), and other technologies.


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Main parameters to guarantee the audio quality of your digital product

Discover the main parameters to guarantee the audio quality of your digital product

Do you know the differences that exist between the formats? Do you understand how the compression rate works?

Audio settings for recorders or sound interfaces can be very confusing. But, if you are going to work with videos or podcasts, it will be useful to know how to interpret the parameters when recording and exporting files, either in Audacity (free), Reaper, Adobe Audition or in video editors.

Here we are going to talk about the differences between sampling rates (sample rate), resolution (bit depth), file compression rates and format variations. Thus, you will be more sure of the options you have regarding audio quality and you can guarantee good results.

In short, you will understand why we recommend recording in uncompressed format (WAV, for example) in 24 bits and 48 kHz. In addition, you will also know why, in most cases, we do not need more than a 192 kbps MP3 to export excellent quality audio.

We will also talk about the possibility of compressing more podcast files, which can be generated in MP3 64 kbps, mono, to facilitate online consumption.

Formats, extensions and codecs: What do they mean?
When it comes to audio files, we can talk about formats, extensions and codecs. In summary, we can say that the format refers to the type of file, identified by its extension (* .mp3, * .wav, * .ogg, * .wma etc), which often tells us how it has been encoded or which It is your codec.

For example, a file in the MP3 format has * .mp3 extension and MPEG-1 Audio Layer III codec.

Examples of audio file extensions

Normally those endings are mixed. But what is important to know is that, as in videos, files with the same type of extension do not always have the same codec and vice versa.

That information is valid so that you do not feel lost in case you do not understand the reason why a software, which normally plays your * .m4a files, does not play another one with the same extension, for example.

Such a situation could indicate that the codecs used are different. In that case, the solution would be to use other software to read the file or to convert it (new encoding). This can be done even in video editors.

The variations of formats and codecs depend on the options of the companies that develop the software that executes the files. In these cases, there are many things at stake, such as technical specifications and relations with patents.

On the other hand, files are usually divided into two types: without compression or compressed.

Files without compression

Audio recording equipment usually offers us options to record files without losing any information. These files, not compressed, can be generated in various formats and extensions, such as WAV, AIFF, FLAC and ALAC. For those who are familiar with photography, they are equivalent to RAW or DNG.

As they are usually very heavy, using lossless formats in the final product is only recommended in some cases, such as:

when the final product can be processed by the consumer (files intended for sound banks, for example);
when there will be recording on physical media (CD, DVD and Blue-Ray);
or for the audiophile market (for a matter of perceived value and high quality assurance).
But, even if you don’t want to end the process with a WAV (one of the most common), lossless formats can be very useful in the editing stage. Because they contain a lot of information, they support more extreme alterations without harming the audio quality.

With plugins, conversions and processing, they can be handled more freely, guaranteeing excellent quality, even if a compressed file is subsequently generated.

Compressed files

Most of the equipment available in the market (cameras, cell phones and even audio recorders) usually delivers already compressed files. This type of file is more practical, easy to process, requires less storage space and has very small sizes (in bytes).

Some examples of these formats are: 3GP, AAC, M4A, OGG, WMA and MP3, which is, without a doubt, the best known. The files are like JPEG or GIF in the field of images.

Through a complex algorithm, these files are generated seeking to keep only relevant information for our ears. Depending on the compression mode, we can generate an MP3 from a WAV and have a file 10 times smaller, without noticeable changes in audio quality.