is lossless audio better Archives - Page 4 of 8

What is lossless sound quality Part 3

Free Download Mp4Gain

What is lossless sound quality Part 3

Apple Music Lossless: What Devices are Supported? - MacRumors

Although the sense of sound can be quantified through data, it has always been a subjective awareness.

Qué es Apple Music sin pérdidas y qué dispositivos funcionan?

However, apart from the difference in the sense of human hearing, the quality of each piece of music still goes back to the original recording and after recording. production; Many years ago, Sony started promoting high-quality music. When it comes to music and sound quality equipment, the author once talked to a senior engineer at Sony about the difference high quality sound makes to the listener. At that time, the senior engineer pointed out that from the data plane, the high-quality sound format is actually a large extension of high-frequency. However, if you ditch the data specs and record high-quality music with modern equipment, you’ll be able to present deeper, more realistic low-frequency dynamics.

The photo contains electronic accessories, electronics, Sony Walkman NW-WM1 series, Sony DMP-Z1, headphones

▲Although the quality of the original sound is very important, even a well-recorded 320K file with a good playback and listening device can work better than directly using a mobile phone to play a high-quality file with the included headphones

However, this is also seen from the original conditions of the radio equipment, but generally the music released to the market will not be released directly after being picked up. The original audio still needs to go through steps like re-editing, post-production. , synthesis, etc.. The music post-production process will also degrade the sound quality and involve personal preferences. If the editing is excessive, the sound quality will also be affected.

However, if the WAVE format, which is commonly used in standard digital music, is used, no matter what the result of the front recording is and how damaged it is, the music will eventually be compressed into a file with a fixed format. sampling rate, but the content will also include a large amount of inaudible information. ; As for the lossless compression of FLAC, AAC, etc., the sound psychology theory removes information that can be considered non-existent, so that the file can be simplified.

OTOTOY is mentioned in the photo, There is a sound you can’t bru-, Genre Main > Best Selling Album Best Selling EP Latest Release Featured Item Music Information Merchandise Sale IN STORE OTOTOY Academy, including web pages, multimedia, online advertising, computer programs, product

▲ The new generation of recording methods will also use the 24-bit 44.1 kHz or higher format, which can record richer details (Image taken from: Ototoy)

Before we go on to mention high-quality sound, let’s talk about the changes related to recording in recent years; With the improvement of digital recording technology in recent years, the front recording project has also begun to introduce high-quality sound recording to exceed the traditional CD sound quality 16-bit 44.1kHz sampling above 24-bit 44.1 kHz The format is used like the original master tape, although it can only be increased from 16-bit to 24-bit, but the increased amount of data per second means there is more information. If the subsequent sampling rate is increased to 96 bits, the PCM encoded sound curve of the sawtooth waveform can be improved. Close to analog waveforms.

For example, the Japanese digital music platform Ototoy will mark such music based on high-quality recordings with the HQD symbol. Before the term Hi-Res Audio, this type of 24-bit audio based on high-quality recordings and not re-pressed into CD-quality sound. The file is usually completed with a digital mastering level sound quality file, and has been in practice for many years before the appearance of the hi-res level mark. Incidentally, SACDs recorded in 1-bit format and presented in DSD format that is close to an analog curve can also be considered as mastering. It is a kind of high-quality sound quality, but strictly speaking, since the DSD format does not have the editing function, in fact, the DSD file is still converted as a high-density PCM file.

9:41, all colors are mentioned in the photo, including Apple Music Lossless Android, Lossless Compression, Apple Music, Dolby Atmos, 3D Sound

▲Currently, high-resolution music is divided into analog mastering transcription, CD-quality mastering scaling, and high-quality native sound mastering, among which the scaling effect is still the worst

Free Download Mp4Gain

Mp4Gain Main Window

Mp4Gain Features

Free Download Mp4Gain

What is lossless sound quality Part 2

lossless audio

The principle of these audio compression methods is to preserve places that are easily heard by the human ear as much as possible.

Music Lossless

In conventional fixed bit rate (CBR) mode, the audible data in the audio is removed and is easier for the human ear to hear. The more information that is withheld, the less information that is withheld when the part is inaudible. As the complexity of the sound increases, the degree of deterioration in sound quality becomes more apparent. For example, when listening to pure voice Performances and performances combined with background music, pure compressed music for vocals, sounds less degraded than the original file.

As for the lossless sound quality offered by the current streaming platform, there are many formats, but in fact, strictly speaking, these formats, including flac and ALAC, belong to lossless compression (non-destructive data compression) in place of lossless sound quality in a strict sense. The performance is almost the same as WAVE, but the file size is small, the decoding speed is fast, and at the same time, it can be used in streaming services. Therefore, it is also the representative format of lossless sound quality entering the era of non-optical disc media, and it is also the current music streaming service.

In addition, Tidal’s MQA is a more controversial format, because although MQA is general lossless audio reduction, it focuses on making high quality music files higher than CD quality so that they are similar to files. CD-quality flac. original high-quality sound format, but the point of controversy is whether the higher compression ratio can maintain the same real listening experience as the original high-quality sound quality has been controversial, and MQA requires a specific device to perform the hardware decoding. many devices are still only able to do MQA decoding through software.

The photo mentions オーディオ Association が, ハイレゾ対応 machine に, めた processing power, including ハイレゾオーディオ definition, digital audio, high-resolution audio, Japan オーディオ Association, sound quality

▲Today’s so-called High-Resolution Audio generally refers to sound quality above CD, but to be certified, the device must support 24-bit, 96kHz format processing capability.

However, since MP3 and AAC are previously planned destructive music compression formats, their purpose is to compress CD-level sound quality into smaller files, so most of the encoding specifications are presented in one presentation. 16-bit 44.1 kHz or 16-bit 48 kHz CD-level audio, but MQA is a format with a reduced file size that blocks high-quality sound. Basically, the MQA format will be equivalent to PCM 24-bit or top music.

In fact, with that said, current music file formats that don’t emphasize high-quality streaming services, whether presented in MP3 or AAC, are called lossy-compressed music, while high-quality, lossless streaming quality is compressed without loss. music. As for the music heard by traditional vehicles like vinyl and CD, it is called lossless music. In theory, non-destructively compressed lossless music and lossless music should have the same sound quality.

Does lossless sound quality have to be good? Does compressed sound have to be bad?
The photo mentions Browse, Coming Soon, New Single, and Apple. Related, contains media, streaming, apple, eddie library, media

▲ Although Apple Music has released lossless sound quality, its marketing focus is on spatial audio

When the Japanese audio industry started promoting high-quality music, many people jumped up and said that high-quality sound was useless. When Apple Music launched the premium sound format, its executives also said that he was one of the people who couldn’t tell the difference, noting that Apple launched the premium sound service to serve one of those hundred people. ; Before we talk about high-quality sound, let’s go back and talk about the current state of digital music on today’s playback devices. .

What is lossless sound quality

There is no comparison, no harm, if lossless sound quality and high sound quality are necessary, and what differences in hearing can Bit-Perfect bring without going through SRC

lossless & lossless audio

mp3

KKBOX

flac

spotify

high resolution

dolby atmos

Apple

apple music

CAA

360 reality audio

SRC

spatial audio

Bit-Perfect

Although lossless sound quality and high-quality streaming services have been on the market for a while, as have true wireless earphones, Apple isn’t the first to make waves in the market, with Apple’s launch of so-called high-fidelity compressed sound quality. in Apple Music, in fact, after the lossless compression commonly known in Taiwan’s audio industry, lossless sound quality and high sound quality have instantly become a hot topic discussed by many people, but if the benefits of lossless sound quality are really obvious, the author will spend some space from the theoretical concept to the practical level. The differences are briefly described, but the following arguments focus on being easy to understand, so some of the descriptions are not entirely accurate.

What is lossless sound quality? What is the sound quality of the music we usually listen to?
The photo mentions * Introduction to KKBOX sound quality (including format), release year, sound quality, including digital, KKBox, streaming, Hi-Res Audio and Hi-Fi

▲ Both AAC and MP3 are destructive compression, while FLAC and ALAC are lossless compression

Before we go into the details, let’s talk about what is called lossless sound quality; From the author’s concept and cognition, the so-called lossless sound quality is a relative word rather than an absolute word. The main source is the relative word born due to the emergence of the MP3 music compression format. ; After the music industry entered the digital format, digital music files were generally recorded through PCM encoding, and WAVE files were generally used on CDs. The time and space situation of MP3 was Due to the fact that the capacity of the hard disk was generally not large at that time, in order to be limited in the limited space, a large amount of music data is stored in the storage space and you may need to compress the files. .

The reason why MP3 cannot be called a lossless format is because its essence is to compress the original WAVE file with a limited bit rate by combining concepts such as the psychology of sound. In bitrate compression mode, compared to the original WAVE file, the bitrate is at least 1:4 to 12:1. The higher the bitrate, the greater the amount of information retained. For example, AAC format also uses similar audio psychology for compression, but the efficiency is better than MP3. Therefore, the lossless sound quality of most streaming platforms today is mostly AAC as the mainstream.

Photo mentions KKBOX, FLAC format, 16bit/48kHz, related to KKBox, including kkbox Hi-Res, Hi-Res Audio, KKBox, Streaming Media, Hi-Fi

▲ Although the waveform of digital music in PCM format will appear jagged, but as the sampling rate increases, it will be closer to the analog arc curve

What is lossless? Part 3

Apple Music lossless

AAC abbreviation

Advanced Audio Coding. Lossy compressed audio file format used by the iTunes Store. The extension is “.m4a”. One of the audio data compression methods included in the video data succeeding MP3 (MPEG-1 Audio Layer-3), which is a method of compressing audio data. The number of quantization bits/sampling rate supports up to 24 bits/96 kHz. However, due to lossy compression, the sound quality is lower than lossless or uncompressed audio files. Also, because it is a lossy compression, it is not called lossless or high resolution.

If I compare AAC with a letter,
I wrote a message on a new sheet of paper, but I wanted to inform the other party of the important things as soon as possible, so I cut the “beginning/end” of “beginning/middle/end” with scissors and only the ” naka”. To pass to The person receiving the letter reads the letters without knowing what the new paper and “Begin/End” text is like.

● Click here for a more detailed explanation of the above audio codec.

■ An audio codec is
a device or software that encodes sent data in the format of an audio file and decodes the encoded data back to its original state.

Let’s compare the sound quality.
How do you listen to “ALAC lossless”, “ALAC hi-res” and “AAC”? This time the singer-songwriter Moeka Giga appeared and she made us experiment listening and comparing the sound quality. We will deliver a realistic voice of Moeka Giga, if the way the sound is actually heard differs depending on the format of the sound source.

What is lossless? Part 2

Lossy compressed sound source ⇒ Typical format: AAC, MP3

Lossless Aplee Music

Lossy Compressed Sound Font Illustration
A format that cuts out sounds that are difficult for human audiovisual to hear and compresses the capacity to a small size. Sound quality is sacrificed and deteriorated by that amount. Since the data is actually cut, once compressed, the original sound quality will not be restored even if you return to the uncompressed format.

■ What is compression?:
Reduce the capacity of data that contains a large amount of information and preserve it as much as possible.
Also, compression can reduce the load on the terminal, but the quality is lower than the original information because the capacity is reduced.

audio codec
Abbreviation for ALAC
Apple Lossless Audio Codec. Lossless compression audio file format used in “Apple Music” music and video distribution service developed by Apple and iTunes in media player. The extension is “.m4a”. The number of quantization bits is 16, 20, 24, 32 bits. The sample rate supports from 1kHz to 384kHz. (In OTOTOY, the number of quantization bits/sampling frequency supports up to 32 integer bits/384 kHz)

If you compare ALAC with a letter,
write a message on new paper, fold it vertically and hand it to the other party. The person receiving the letter can open it when he knows that it is folded once vertically. However, after the paper is folded, a single wrinkle is formed, and although it cannot be read in the state of new paper, the characters can be read firmly.

Abbreviation for FLAC
Free Lossless Audio Codec. A lossless compressed audio file format provided free of charge. The extension is “.flac”. The number of quantization bits is from 4 bits to 32 bits. The sample rate supports from 1 Hz to 655.3 kHz. (In OTOTOY, the number of quantization bits/sampling frequency supports up to 24bit/192kHz)

If you compare FLAC with a letter, the
situation is similar to ALAC. To explain the difference, FLAC is a state where the card is folded sideways. Also, the recipient can tell that it is folded to one side and open it.

WAV
A type of RIFF (Resource Interchange File Format), which is an audio file format jointly developed by Microsoft and IBM, and defines a method of storing various data in a file. It is generally an uncompressed audio file format, but the data format is free and it is also possible to store compressed data such as MP3 and WMA. In RIFF, the identifier is “WAVE”, but the extension is “.wav”, and it has come to be called WAV to distinguish the pronunciation sound from the web.

If you compare WAV with a letter,
write a message on new paper and deliver it to the other party without wrinkles. The person receiving the letter can read the letters in new paper condition.

What is lossless?

lossless

In June 2021, Apple Music lifted the ban on hi-res and lossless, with “lossless” attracting attention.

LOSSLESS

Do you correctly understand the meaning of the word “lossless” when looking at this page? What does “lossless” mean here? Higashihara, a new editor, had doubts about the meaning and sound quality of the word “lossless”, so I did some serious research. We also have a sound source that you can download for free, so let’s get to know each other while listening to them.

sound quality

Sound source data equivalent to a lossless CD sound source (16-bit/44.1 kHz). There are uncompressed sound sources and lossless compressed sound sources that can be compressed and stored without deterioration. In the sense that there is no “loss” due to compression (less), CD sound quality data is generally referred to as such.

Sound source data with a quantization bit rate/sampling frequency (24 bit/44.1 kHz or higher) that exceeds Hi-Res CD sound source (16 bit/44.1 kHz). For that amount, the capacity will be larger than the CD sound quality sound source data, but since the data can express more delicate expressions, a deeper sound can be heard.

● Click here for a more detailed explanation of the above high resolution.

■ The sound quality is
sound and voice quality. Sound has the following three aspects, and sound quality is determined by exerting these properties on each other.
1. Aspects such as physical signs
2. Aspects of auditory psychoacoustics of hearing humans
3. Aspects of expression expressed by a collection of sounds such as voice and music

Also, the following three units are important for measuring sound quality. ..

(1) bit (quantization bit number)
A value that shows how precisely the intensity of the sound can be expressed (large and small). The lower the number, the smaller the sound will be recognized as noise, and the higher the number, the more detailed the sound will be reproduced.

(2) kHz (sampling frequency)
A value indicating how many times per second the original sound is sampled (sampled) when digitizing. The greater the number of samples (the larger the value), the finer the data can be.

③ Bit rate
Abbreviation for bit per second. A value indicating how much data was transferred per second when sending and receiving data. If the pulse rate is high, a lot of data can be transferred and smooth data can be received, and if it is low, little data can be transferred and the data will be interrupted.

compression performance
Reversible compression sound source ⇒ Representative form な: ALAC, FLAC

Lossless compressed sound source diagram
* This diagram shows the quality of the sound when it is compressed and then uncompressed.
A data format that reproduces the quality of the original sound by reducing the storage capacity (compression) of the sound source data according to the rules of each format (codec) and expanding it according to the playback rules. It has less capacity than the uncompressed format, but it cannot reduce data capacity as much as the lossy compressed format. Since data capacity can be reduced without degrading sound quality, this compression format is often used when dealing with lossless (CD-equivalent sound quality) and high-resolution sound sources.

Uncompressed sound source ⇒ Typical format: WAV, AIFF

Uncompressed sound source diagram
The original data format of CD sound quality (16 bit/44.1 kHz) and high resolution (24 bit/44 kHz or higher). You can of course listen to the sound quality as it is. In the old days, the amount of data was said to be relatively large depending on the compressed sound source, but that was 20 years ago too.

The “good sound” experience of Apple Music will change! Part 2

The “good sound” experience of Apple Music will change! Part 2

How to Enjoy Lossless Audio on Your iPhone or Mac
Learn how to create an environment to enjoy “good sound” with lossless audio from Apple Music.

First, the staples of player playback are the iPhone, iPad, Mac, and Apple TV. When listening with HomePod, high-quality sound reproduction in compressed AAC format will be performed at the beginning of the service, but it appears that lossless support via software update is planned in the future.

You can also enjoy lossless audio with the Android version of “Apple Music App”. The browser version of Apple Music does not support either of the two new services as of June.

The first way to enjoy Apple Music lossless audio on your iPhone, iPad, or Mac is to “listen to the built-in speakers.” In particular, the new iMac has an integrated sound system consisting of six speaker units and an amplifier, which should make Apple Music’s lossless audio sound powerful.

With a powerful sound system, the iMac pairs well with Apple Music’s lossless surround audio services.

While it seems that you can enjoy powerful sound even with iPhone and iPad speakers, it is not suitable for listening while moving when you go out. I would like to listen using the AirPods series which is more compatible with each one, but since the Bluetooth audio codec compatible with the iPhone and AirPods series cannot transmit while maintaining the quality equivalent to lossless playback, compression will be applied. In that case, it would be more efficient to listen to the original AAC format distribution.

If you want to enjoy lossless audio on your iPhone or iPad, you can use headphones that can be connected to Lightning, such as the wired “EarPods with Lightning connector” headphones that are currently sold as an option. Alternatively, you can listen with analog-connected wired headphones or with headphones through an adapter with a built-in DAC, such as the Lightning / 3.5mm Headphone Jack Adapter. Also, if you use a headphone amplifier with a built-in USB-DAC function released by audio manufacturers, including Mac, you can enjoy richer lossless audio reproduction.

It is convenient to have a DAC-equipped headset that can be connected directly to the Lightning terminal.

For Apple TV, you can enjoy lossless audio by connecting it to a sound bar or surround sound amplifier with an HDMI cable. Ideal when you want to listen to music slowly in a home theater or audio room.

Many Android devices are equipped with a 3.5mm headphone jack, so you can create a lossless audio playback environment more easily.

Also began the distribution of “high resolution” beyond the losses without losses.
The lossless distribution of Apple Music includes files provided at 44.1 kHz / 16-bit, which has the same sound quality as a CD, and 48 kHz / 24-bit, which Apple calls “lossless with a sound quality greater than that of a CD “. The latter appears to have more than 7 million titles. You can check the detailed information of the song by touching the “Lossless” badge displayed on the music app’s playback screen.

The “good sound” experience of Apple Music will change!

The “good sound” experience of Apple Music will change!

lossless audio

Explaining the charm of the lossless environment

Hear studio-produced sounds with more luxurious sound quality
How to Enjoy Lossless Audio on Your iPhone or Mac
Also began the distribution of “high resolution” beyond the losses without losses.
Enjoy immersive playback with Apple Music
Compatible with various headphones / earphones and sound bars
“Good sound” is the standard for Apple Music sounds you hear on your iPhone.
Starting in June, two new “good sound experiences” will be added to Apple Music, Apple’s flat-rate music distribution service. “Lossless Audio” and “Dolby Atmos Spatial Audio”. I would like to explain the contents of the service and the environment necessary to enjoy it.

We’ll explain the new “lossless audio” and “Dolby Atmos spatial audio” added to Apple Music.

Hear studio-produced sounds with more luxurious sound quality
Currently, the sound quality of Apple Music can be listened to while reducing the consumption of data capacity by using mobile communication transmission by iPhone / iPad while maintaining the quality of the sound source produced by the creator in the studio. to the user’s hand as It is. It is balanced and distributed as a 256 kbps AAC format file.

Newly added lossless audio is a technology for enjoying music playback in true-to-original sound quality, without loss due to compression processing. Apple Music uses “ALAC” (Apple Lossless Audio Codec), a lossless compression codec system that can be compressed and then decompressed while ensuring the quality of the original sound source.

As of the end of May 2021, Apple Music has more than 75 million songs distributed, but all songs in the catalog will be available in lossless audio, except for radio audio and music video. This Apple Music update will be available to subscribers in all 167 countries and territories around the world for the same monthly fee.

Apple Music is currently deployed in 167 countries and regions around the world. You can enjoy it at the same price even after adding a new service.

Enjoying lossless audio is very easy. For iPhone / iPad, you will be able to select lossless sound quality for mobile communication transmission, Wi-Fi and download in “Music” of the settings application. The default setting is “Off”, so you must set the necessary parts for each of the three listening methods to lossless.

Even if the lossless audio service starts, you can still choose to deliver in the traditional AAC format. This is because if you select lossless audio, especially in a mobile communication streaming environment, the bit rate will reach 1.4 Mbps or more during playback, and it will “gig down” at a faster speed than before. .

You can also download the songs you want to listen to on a device like an iPhone with lossless quality and listen to them offline. However, even in this case, the size of the lossless data will be larger than the distribution file in normal AAC format, so it seems necessary to adjust it according to the storage capacity of the iPhone or iPad.

Audio and video analogic & digital

Audio and video analogic & digital

Lossless and Lossy audio compression

The appearance of multimedia systems, of course, brought about revolutionary changes in areas such as education, computer training, in many areas of professional activity, science, art, computer games, etc. But, you must agree, it is impossible to imagine the modern. multimedia systems without sound or video. In this work, I would like to dwell on the consideration of the fundamental differences in the representation of digital signals from analog, the characteristics of digital audio and video information, their compression algorithms (compression).

Lossy, and Lossless compression

2. Differences between the digital representation of analog signals.

The traditional analog representation of signals is based on the similarity (similarity) of electrical signals (current and voltage changes) with the original signals represented by them (sound pressure, temperature, speed, etc.), as well as on the similarity of electrical signals. signal forms at various points in the transmission or amplification path. The shape of the electrical curve that describes (also called transfer) the original signal is as close as possible to the shape of the curve of this signal.

Such a representation is the most accurate, however, the slightest distortion of the shape of the electrical carrier signal will inevitably involve the same distortion of the shape and signal of the carrier. In terms of information theory, the amount of information in the carrier signal is exactly equal to the amount of information in the original signal, and the electrical representation does not contain redundancy that could protect the carried signal from distortion during storage, transmission. and amplification.

The digital representation of electrical signals is designed to add redundancy to avoid unwanted interference. For this, serious restrictions are imposed on the carrier electrical signal: its amplitude can take only two limit values: 0 and 1.

In this case, the entire zone of possible amplitudes is divided into three zones: the lower one represents zero values, the upper one, individual, and the middle one is prohibited, only interferences can enter. Therefore, any interference, the amplitude of which is less than half the amplitude of the carrier signal, does not affect the correct transmission of the values 0 and 1. Interference with a higher amplitude also does not affect whether the duration of the interference pulse is significantly shorter than the duration of the information pulse, and a filter is installed at the pulse noise input of the receiver.

The digital signal formed in this way can carry any useful information that is encoded in the form of a sequence of bits: zeros and ones; Electrical and sound signals are a special case of such information. Here, the amount of information in the digital carrier signal is much greater than in the original encoded signal, so that the carrier signal has some redundancy with respect to the original, and any distortion in the waveform of the carrier signal, which it still retains the ability of the receiver to correctly distinguish between zeros and ones, it does not affect the reliability of the signal transmitted by this information signal. However, in the case of significant interference, the shape of the signal can become so distorted that the precise transmission of the information being carried becomes impossible: errors appear in it, which, with a simple coding method, the receiver does not you can only correct, but also detect. To further increase the resistance of a digital signal to interference and distortion, two types of redundant digital coding are used: verification codes (EDC – Error Detection Code) and correction (ECC – Error Correction Code) . Digital encoding is simply adding extra bits to the original information and / or converting the original bit string into a longer string and other structure. EDC allows you to simply detect the fact of an error: a distortion or loss of a useful one or the appearance of a false digit, but the information transferred in this case is also distorted; ECC allows you to immediately correct detected errors, keeping the information that is transferred unchanged.

Each type of EDC / ECC has its own capacity limit to detect and correct errors, after which undetected errors and distortions of the information being transferred start anew. An increase in the amount of EDC / ECC relative to the amount of initial information generally increases the detection and correction capabilities of these codes.

Like EDC, the popular cyclic redundancy code CRC (Cyclic Redundancy Check), whose essence is the complex mixture of the initial information in the block and the formation of short binary words, whose bits have u

Audio compression algorithms for streaming purposes

Audio compression algorithms for streaming purposes.

Lossy, and Lossless compression

The problem of transmitting the necessary number of audio channels through a network of limited capacity forces us to resort to audio compression.

Lossy and Lossless ata compresion in digital audio

Despite the use of modern digital technologies, compression negatively affects sound quality and causes additional delay in signal transmission.

Currently, there are two fundamentally different approaches to compressing audio signals. This article will provide a general comparison between these two different compression principles. Also presented are graphs of the frequency response (amplitude frequency characteristic) of the sound sample in its original uncompressed form and after one cycle of encoding and decoding using MPEG Layer II and Enhanced apt-X.

Algorithms like MPEG and AAC use encoding using a psychoacoustic model of sound perception. Another approach is time encoding using Adaptive Differential PCM (ADPCM) in algorithms like Enhanced apt-X.

Linear PCM audio
Before compression, the audio is generally digitized in linear PCM format at 32 kHz, 44.1 or 48 kHz with a resolution of 16 or 24 bits.

The analog signal will be digitized in uncompressed digital PCM. The digital inputs of the codecs use oversampling to ensure conversion without timing issues. The uncompressed PCM signal is our benchmark for comparing compressed audio files.

MPEG Layer ll compression
MPEG 1 Layer ll is a widely used format. This is a typical example of a psychoacoustic perception coding algorithm that analyzes the incoming signal and compares it to a theoretical model to determine what frequency and what time domain information can be lost. The need to analyze the audio signal results in a mandatory delay, typically greater than 30 ms.

In theory, high compression ratios can be achieved, but even with relatively low compression, MPEG can seriously degrade audio quality. In Fig. 2 shows the frequency response after one pass of MPEG encoding of the source file.

Be aware of frequencies that are lost or distorted compared to original PCM audio.

Compression Enhanced Apt-X
Enhanced apt-X uses ADPCM audio processing technology. The signal is divided into four frequency bands that can be processed at a quarter of the original sample rate using a variable bit rate and variable quantization step. Since all processing is based on the time domain method, there is no delay other than the actual processing time required.

As a result, a 4: 1 compression ratio preserves the entire frequency content of the original signal with a coding delay of less than 3 ms. Frequency response graph in Fig. 3 shows the result of one pass encoding / decoding using Enhanced apt-X at 256 kbps and illustrates the high fidelity of Enhanced apt-X compared to the original uncompressed signal.

How Enhanced apt-X Works
The improved apt-X encoding algorithm passes the original PCM data through a specially designed two-stage Q-mirror filter to divide the signal into four subbands and reduce the clock frequency to 1/4 of the original clock frequency. The quantization procedure consists of processing four sub-signals to reduce each signal from 16 bits to 7 bits in subband 1, 4 bits in subband 2, 3 bits in subband 3 and 2 in subband 4.

The inverse quantizer and prediction scheme uses the above values to predict the size of the next signal. This value is compared to the actual signal and the “difference” is measured. The encoder transmits this measured “difference” signal to the decoder. Each subband is processed in parallel and the output of the string quantizer and predictor is encoded with a predetermined resolution. The processing output of the four subbands is multiplexed into a single 16- or 24-bit enhanced apt-X signal. Then additional data and sync data is added to it for streaming.