Lossless audio compression


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Lossless audio compression

Lossless Audio compression

FLAC is perhaps the most popular lossless audio format and encoding codec. Music lovers are gradually switching to this format. WavPack competes with it, but it is not that popular. It’s the same story with Apple Lossless, which reduces the size to 60%.

Lossy file compression

The story here is: quality is better and size is bigger.

Skeptics say that it is almost impossible to distinguish MP3 (320 kbps) from Losless by ear. “And if there is no difference, why pay more?” In fact, on ordinary equipment, it is quite difficult to feel the difference in audio formats, even for music lovers. But there are those who immediately feel this difference (they personally attended the experiment). But when listening to a good device, the difference is huge. The problem is that not everyone can afford a good device.

In what format and with what quality is music heard on the radio?
In fact, we can say that there are currently two main audio formats: lossy (compressed) and lossless (uncompressed). They are classified into many types.

Lossy takes up less disk space, but degrades the quality of the audio track. When compressed using the MPEG protocol (hence the name mp3 – mp4 for files containing video sequences), the hues and transition tones, which are barely noticeable to the ear, are cut off. This makes the file clearer, but it also degrades it. The last place is occupied by the bit rate of that file: the degree of compression of each second of the audio track. The lower the bitrate, the less space the file will occupy and the worse the quality. Thus, a composition of three minutes in mp3 with a bit rate of 320 kilobits per second will occupy up to 3 megabytes on disk; a similar composition with a 96 kilobit bit rate will occupy about 400 kilobytes.

Lossless is as close to the original analog sound * as possible, making it much loved by sound engineers. Lossless formats take up much more disk space even compared to mp3-320. Among these formats, the most common are WAV (standard), FLAC (economic), AIFF (Apple). The former is used most often.

Professional sound recording is done only in uncompressed format. Only with him do the sound engineers work.

On the radio, the situation is somewhat more complicated. This is due to the peculiarities of the work of the media, namely efficiency and commercial profitability. The use of high-capacity servers is expensive and therefore most radio stations encode audio tracks in mp3 format at a bit rate of 256 kilobits per second. However, this is typical mainly of national stations. Equipment purchased from abroad has standard configurations that assume WAV encoding.

Why are software developers focusing on WAV? Because the radio signal cannot propagate without interference. Therefore, the listener still receives a small and sometimes significantly distorted signal. Therefore, broadcasters are faced with a reasonable question: what quality of sound will the listener perceive best: distorted ideal or distorted distortion? For this reason, in Europe and the United States, the WAV standard (AIFF, if the station operates with Apple equipment) is adopted, in Russia – mp3 with a bit rate of 256 kilobits per second.


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What methods are used to effectively compress digital audio?

What methods are used to effectively compress digital audio?

Digital audio Compresssion

Currently, the most famous are Audio MPEG, PASC and ATRAC. All use the so-called “perception coding” (perceptual coding), in which information that is barely perceived by the ear is removed from the sound signal.

Audio compression

As a result, despite the change in the shape and spectrum of the signal, your hearing perception is practically unchanged and the compression ratio justifies a slight decrease in quality. Such encoding refers to lossy compression methods, when it is no longer possible to accurately restore the original waveform from the compressed signal.

Techniques to remove some of the information are based on a characteristic of human hearing, called masking: if there are pronounced peaks (dominant harmonics) in the sound spectrum, the weakest frequency components in the immediate vicinity of them are practically not perceived (masked) by ear. During encoding, the entire audio stream is divided into small frames, each of which is converted into a spectral representation and divided into several frequency bands. Within bands, masked sounds are detected and removed, after which each frame undergoes adaptive coding directly in spectral form. All these operations make it possible to significantly reduce (several times) the amount of data while maintaining the quality acceptable to most listeners.

Each of the described encoding methods is characterized by the bit rate at which the compressed information must enter the decoder when the audio signal is recovered. The decoder converts a series of compressed instantaneous signal spectra into a conventional digital waveform.

Audio MPEG is a group of audio compression techniques standardized by MPEG (Moving Pictures Experts Group). MPEG audio methods come in various types: MPEG-1, MPEG-2, etc .; currently the most common type is MPEG-1.

There are three layers of MPEG-1 audio to compress stereo signals:

1 – 1: 4 compression ratio with a data stream of 384 kbps;
2-1: 6..1: 8 at 256..192 kbps;
3 – 1: 10..1: 12 at 128..112 kbps.
The minimum data rate at each layer is defined as 32 kbps; the specified bit rates keep the signal quality close to that of a CD.

All three layers use a frame input spectral transform divided into 32 frequency bands. The most optimal level in terms of data volume and sound quality is recognized as level 3 with a bit rate of 128 kbps and a data density of approximately 1 Mb / min. When compressing at lower speeds, the forced limiting of the frequency band to 15-16 kHz begins, and phase distortions of the channels also appear (effect like a phaser or flanger).

MPEG audio is used in computer sound systems, CD-i / DVD, “audio” CD-ROM, digital radio / television, and other mass audio transmission systems.

PASC (Precision Adaptive Sub-Band Coding) is a special case of Audio MPEG-1 Layer 1 with a bit rate of 384 kbps (1: 4 compression). Used in the DCC system.

ATRAC (Adaptive TRansform Acoustic Coding) is based on a stereo audio format with 16-bit quantization and a sample rate of 44.1 kHz. When compressed, each frame is divided into 52 frequency bands, resulting in a transmission rate of 292 kbps (1: 5 compression). Used in MiniDisk system.

Lossless audio compression explained

Lossless audio compression explained

LossLess Audio compression

FLAC is perhaps the most popular lossless audio format and encoding codec.

lossless audio compression

Music lovers are gradually switching to this format. WavPack competes with it, but it is not that popular. It’s the same story with Apple Lossless, which reduces the size to 60%.

Here the story is exactly the opposite: the quality is better and the size is greater.

Skeptics say that it is almost impossible to distinguish MP3 (320 kbps) from Losless by ear. “And if there is no difference, why pay more?” In fact, on ordinary equipment, it is quite difficult to feel the difference in audio formats, even for music lovers. But there are those who immediately feel this difference (they personally attended the experiment). But when listening to a good device, the difference is huge. The problem is that not everyone can afford a good device.

Compressed using special lossless audio codecs, it can be restored with absolute precision if desired.

If you take a normal audio CD disc with analog sound, record it in WAV format for uncompressed sound, then compress WAV using lossless codec, then decompress the resulting sound file into WAV and burn the result to a blank CD , you can get two completely identical audio files COMPACT DISCS.

The advantage of lossless for storing an audio collection is that the quality of the recordings is much higher than that of lossy codecs and they take up less space than uncompressed audio. It is true that lossy files are smaller than lossless music files. Most modern playback programs understand the lossless format. Programs that cannot play it can easily learn it using the lossless plugin. What are lossless audio formats?

Lossless audio formats
A true music lover is unlikely to be satisfied with the sound of music recorded in Ogg Vorbis or MP3 compression formats. Of course, if you listen to audio recordings on home audio equipment, sound defects cannot be heard with your ear, but if you try to play a compressed file on high-quality Hi-Fi equipment, you will immediately find the sound defects. . Of course, creating a collection of quality music on CD or vinyl is not easy. There is a reasonable alternative to this path for lovers of high-quality sound: lossless music. It can be stored on your PC in a way that allows you to keep the original music settings unchanged, even if compression is applied. In this way it simultaneously solves the problems of high-quality music and its compact storage, since audio equipment for listening (headphones, speakers, amplifiers) is quite affordable.

Uncompressed lossless audio formats:

CDDA is an audio CD standard;
WAV: Microsoft Wave;
IFF-8SVX;
IFF-16SV;
AIFF;
Compressed formats:

FLAC;
APE – Monkey’s Audio;
M4A – Apple Lossless – Apple’s high-quality music format;
WV – WavPack;
WMA: Windows Media Audio 9;
TTA – True Audio.
LPAC;
OFR – OptimFROG;
RKA-RKAU;
SHN – Shorten.
FLAC format
The most common format is the. It differs from lossy audio codecs in that no data is removed from the audio stream when it is used. This makes it possible to use it successfully to play music on Hi-Fi and Hi-End equipment, as well as to create an archive from a collection of audio recordings.

The great advantage of the format is its free distribution. This is important for musicians who record music on their own. The format has grown in popularity lately, thanks to which its support is included in the vast majority of multimedia players.

APE format
Unlike FLAC, for the APE format there are only codecs and plugins for the Windows platform. For other platforms, there are expensive third-party software solutions. The algorithm is capable of achieving lossless compression of the audio information between 1.5 and 2 times. It includes three main stages of encoding, of which only one is based on the use of inherent properties of sound for compression. The rest are similar to conventional filing cabinets. Despite the fact that the compression algorithm is distributed free of charge, the licensing restrictions are such that it is practically inaccessible for amateur musicians.

Apple Lossless Format
You can listen to high-quality lossless music using the audio compression codec without sacrificing Apple quality. This format was developed by Apple for use on its own devices. The format is compatible with iPods with special dock connectors and the latest firmware.