Compress mp3 without losing quality

On lossless music compression, theory, practice, conclusions.
With this material, I want to open a series of articles with everything related to listening to music on a computer. The time has come to share experiences and summarize disparate articles on the Internet in one, although they are not intended to be precise, but relatively brief. In the first part, we will see the audio formats. What is FLAC, WavPack, TAK, Monkey’s Audio, OptimFROG, ALAC, WMA, Shorten, LA, TTA, LPAC, MPEG-4 ALS, MPEG-4 SLS, Real Lossless? Do you know how many types of audio files are registered today? So far, we are dealing with lossless compression formats for audio materials, and the answer to the question about the number of audio extensions is at the end of the article. Happy reading!

So first, let’s define the terms:

“An algorithm is a precise prescription that defines the computational process that goes from variable inputs to the desired result.”

“Codec (codec in English, of encoder / decoder – encoder / decoder – encoder / decoder or compressor / decompressor) is a device or program capable of converting data or signals. Codecs can encode a stream / signal (often for transmission, storage, or encryption) or decode, to view or change into a more suitable format for these operations. Codecs are often used in digital video and audio processing. Most codecs for audio and visual data use lossy compression to obtain an acceptable final (compressed) file size. There are also lossless codecs ”.

“Lossless data compress. – method of data compression, using encoded information that can be restored in one bit. This fully recovers the original data from the compressed state. As a rule, each type of digital information has its own lossless compression algorithms “.

Lossless data compression is used when the identity of the compressed data with the original is important. Common examples are executables, documents, and source code. Programs that use lossless compression formats are called archivers, everyone knows the most popular ZIP or RAR file formats, the Unix Gzip utility, etc. All these programs differ in the applied algorithms (one or more) and therefore in different compression properties of different files.

Part I. – THEORY:

Compression methods or lossless compression algorithms can be classified according to the type of data for which they were created. There are three main types of data: text, images, and sound. Basically any multipurpose lossless data compression algorithm (multipurpose means it can handle any type of binary data) can be used for any type of data, but most of them are inefficient for all basic types. Audio data, for example, cannot be compressed well with a text compression algorithm and vice versa.

Compression methods include the following: entropy compression, dictionary methods, statistical methods. Each method is good for a specific type of data and includes several algorithms.

Entropy compression: Huffman algorithm Adaptive Huffman algorithm Arithmetic coding (interval Shannon-Fano algorithm) Golomb codes Universal Delta code (Elias Fibonacci)

Dictionary methods: RLE Deflate LZ (LZ77 / LZ78 LZSS LZW LZWL LZO LZMA LZX LZRW LZJB LZT)

Statistical algorithm models for text (or textual binary data as executable) include: Burrows-Wheeler transform (block sort preprocessing that makes compression more efficient) LZ77 and LZ78 (used by DEFLATE) LZW.

Thanks to MP3 we can listen to our favorite music everywhere. When you put your MP3s on a USB stick, you can listen to your favorite music in the car, for example. But you can also put MP3 music on your smartphone. Allowing you to listen to music whenever possible.

But sadly, it still happens that the quality of an MP3 is not really what it should be. In this article, we look at the options to solve that problem. So that you can not only listen to music everywhere, but also enjoy it everywhere.

What exactly is an MP3 music file?

Mp3 is a method of compressing digitally stored music. Uncompressed storage of a stereo digital music file takes up a lot of disk space. An average of 10MB of disk space per minute of recorded music.

However, compressing a music file and saving it as MP3 will leave only one-tenth the size of the original file.

Since the introduction of the CD, music has been recorded digitally in the form of samples or measurements. Sound is neither more nor less than vibrating air. These vibrations are also known as sound waves. Sound waves can be measured, recorded, and stored.

However, when sound waves are produced creatively, then it is music.

The number of vibrations per second determines the pitch of the sound. A large amount of vibrations creates a high tone, a small amount of vibrations for a low tone.

The number of vibrations per second is expressed in hertz. The human ear can perceive sounds between 20 Hz and 20,000 Hz.

It was once scientifically discovered that in order to record the highest pitch, a measurement must be taken 44,100 times per second. Therefore, the number 44,100 is the sample rate in hertz that is required for good quality recording.

In addition to high and low tones, a piece of music also contains high and soft passages. The difference between the loudest and the softest passages is called the dynamic range. For the dynamic range of a piece of music to be recorded digitally, you can choose 256 steps (8-bit) between the softest part and the hardest part or 65536 steps (16-bit).

The dynamic range is highest when recording with 16-bit samples or 65536 steps.

If we then do some math with this data, we see that 44,100 measurements are needed for one second of music. Each measurement (sample) is 16 bits (2 bytes) in size. That means 1 second of music takes up 88,200 bytes or 88Kb of disk space.

But since we like to listen to music in stereo, we can multiply that number by 2. For example, one second of music in stereo takes up 176 Kb of disk space and therefore 10 MB per minute.

When a compressed MP3 file is created from an original music file, this is done using a lossy compression method.

Lossy compression causes data loss. With an MP3 file, this means that information is omitted from the file that is beyond the reach of the human ear.

Humans are most sensitive to sounds between 2 kHz and 4 kHz. And we cannot hear loud and soft sounds simultaneously. Therefore, it is only necessary to keep the loud sound. In technical terms, this is called psychoacoustic masking.

What determines the quality of an MP3?
The MP3 format was developed by the German research institute Fraunhofer ISS. In addition to utilizing the limitations of human hearing just mentioned, the format consists of several mathematical formulas. This makes it possible to reduce the original file by a factor of 3 to 12.

The degree of compression is related to the bit rate. Bit rate is the amount of data that is processed per unit of time. This means, among other things, that the more data there is in one second of music, the larger the MP3 file will be. But also the better the sound quality of the MP3.

A bit rate of 64 to 96 kbps is enough to talk. A bit rate of 128 kbps is used for a good quality music file. Excellent quality can be achieved with a bit rate of 192 kbps or higher, with a maximum bit rate of 320 kbps.

A bit rate of 192 kbps or higher is only useful if the recording quality of the track is also excellent.

Obviously if you want the mp3 to sound even better, use Mp4Gain to mormalize mel volume, to correct the equalization and to make a series of changes or improvements.

When it comes to the subject of “MP3 and sound quality”, one is entering a minefield. Hi-fi fundamentalists claim that many people no longer know what good sound really is because of MP3s. The accusation is not entirely unfounded, because MP3 is a lossy format. However, you shouldn’t make it too easy for him with judgment. After all, there is no uniform standard for MP3 quality. Another important question is: what about the sound quality of other formats?

What “lossy” means for the sound quality of an MP3 file

MP3 and other lossy audio formats such as AAC may have been lost. to. designed with the aim of saving storage space. Because at the time of its development, the storage capacity of hard drives was much more limited than it is today, and the download and upload rates were also insufficient for large amounts of data. Today, the bandwidth for streaming and wireless transmission over Bluetooth are limiting factors. So compression still has to be. How is the amount of data reduced compared to the original recording?

On the one hand through compression and on the other hand through the omission of certain sound information. Because not everything that is captured in a recording also becomes the compressed file. To limit the effects of data loss on MP3 quality, only information that is acoustically insignificant is ignored. To be more precise: particularly low frequencies and particularly high tones are cut off. Because people can only perceive extreme highs and lows up to a certain point or not at all.

That’s how high MP3 quality really is

A general evaluation of the quality of MP3 sound is complicated by the fact that there are different levels of quality. They are the result of the respective bit rate (data rate, “bit rate”), specified in kilobits per second (“Kbit / s”). 64 Kbit / s as well as 128, 192, 256 or 320 Kbit / s can be implemented. The following applies: The higher the value, the less data loss will be compared to the source material.

A rule that is mentioned from time to time states that from a bit rate of 192 kbit / s data loss is no longer important for auditory impression. The file format alone says little about the quality of the audio signal.

But there is no clear limit. Factors like music genre, system, and last but not least individual hearing all play an important role when it comes to evaluating the quality of an MP3 file. There are also differences between the audio formats: a file encoded in AAC at 192 kbps tends to provide a better listening experience than an Ogg Vorbis file with the same data rate.

What is the sound quality on Spotify and other music streaming services?

Some 20 years after its invention, MP3 is still the most widely used audio format on the Internet. However, there are other formats that play an important role in music playback today. An example of this is the patent-free Ogg Vorbis format mentioned above. The streaming giant Spotify also relies on this.

Other audio formats used by streaming services are:

• Apple Music: AAC
• Spotify: Ogg Vorbis
• Google Play Music: MP3
• Deezer HiFi: FLAC

Streaming providers are quite reluctant to provide information on the respective data rates. When the service launched, Apple Music announced that the streams would be streamed at a bit rate of 256 kbps. With Spotify it is 320 Kbit / s with high sound quality, also with Google Play Music. At lower quality levels, the bit rate drops below 200 Kbit / s. However, providers of lossless transmission clearly exceed these values: Deezer, for example, announces its high fidelity subscription with 1,411 kbit / s. The stream here is in lossless FLAC format.