What exactly is lossless audio quality?A test to check if you can you hear the difference?

For audiophiles, "Lossless Audio" is not a novel concept. However, as mainstream streaming platforms like Apple Music and Spotify race to introduce this service, lossless audio has gradually become a focal point for the general public. Although various platforms claim to provide lossless audio, their technical specifications and naming standards vary. This article aims to explore the precise definition of lossless audio, its technical principles, and the compatibility and limitations of playback equipment.

To understand lossless audio, one must first clarify the storage mechanism of digital audio files. The distinction between lossless and lossy depends on whether the audio file is "compressed" and the "type of compression algorithm" used.

Early on, restricted by network bandwidth and storage costs, engineers developed lossy compression technologies like MP3 and AAC. These technologies utilize psychoacoustic models to remove high-frequency signals difficult for the human ear to perceive or frequency bands that are masked. While this significantly reduces file size, it also leads to the permanent loss of original audio information, resulting in a collapsed soundstage and diminished detail.

In contrast, lossless audio mainly covers the following two forms:

This is the raw form of digital recording, where analog signals are converted to digital signals and stored directly without any compression processing. It can be viewed as a complete copy of the studio master tape. Common formats include WAV and AIFF. Its advantage lies in the purity and integrity of the sound quality, but the file sizes are massive, demanding significant storage space and bandwidth.

This is currently the mainstream format for streaming media. It is encoded using algorithms such as FLAC or ALAC. The principle is similar to ZIP compression for computer files; although the file size is reduced (typically by 40% to 60%), upon decoding and playback, the data can be restored 100% to the original waveform, ensuring no bit-perfect information is lost.

In summary, the core definition of lossless audio lies in the complete preservation of all acoustic details captured in the studio during the digitization process, without sacrificing any frequency response for the sake of capacity.

When discussing lossless audio, CD quality is usually taken as the benchmark specification. This specification consists of two key indicators:

Determines the dynamic range of the audio, which is the resolution between the loudest and quietest sounds. The standard CD specification is 16-bit.

Determines the frequency response range of the audio, which is the number of times the sound wave is sampled per second. The standard CD specification is 44.1 kHz.

Generally, the maximum bitrate for MP3 format is only about 320 kbps, meaning a large amount of original data has been cut. In comparison, the bitrate for standard CD lossless audio is approximately 1411 kbps. This difference of more than four times the amount of information is the main reason why lossless audio can present richer details and layers.

"Lossless Audio" and "High-Resolution Audio" are often confused, but there is a hierarchical difference in their technical definitions.

Usually refers to audio that meets CD specifications (16-bit / 44.1 kHz). This is the benchmark currently used by streaming services to distinguish from lossy compression formats and to emphasize quality equivalent to physical records.

According to the definitions by Sony and the Japan Audio Society, its specifications must be superior to CD quality. It generally refers to specifications of 24-bit / 96 kHz or 24-bit / 192 kHz and above.

Theoretically, High-Resolution Audio possesses higher information density and more natural reverberation performance. However, in terms of actual listening experience, the perceptibility of the difference is highly dependent on the quality of the recording source, the grade of the playback chain, and the listener's auditory sensitivity.

To help readers quickly understand the technical parameters and characteristics of different audio specifications, they are summarized in the table below:

Specification Type	Common Formats	Bit Depth / Sample Rate	Typical Bitrate	Compression Characteristics & Listening Experience
Lossy Compression	MP3, AAC, OGG	Usually below 16-bit	Below 320 kbps	Destructive compression. Removes some high frequencies and details; sound feels flatter with less spatial sense.
CD Lossless Audio	FLAC, ALAC, WAV	16-bit / 44.1 kHz	Approx. 1411 kbps	Lossless retention. Data is fully restored, sound quality is pure and consistent with physical records.
Hi-Res Audio	FLAC, ALAC, WAV, DSD	24-bit / 96 kHz and above	2000 kbps to >9000 kbps	Extreme detail. Massive dynamic range, capable of presenting minute "airiness" and reverberation of the recording site.

With the popularity of digital streaming technology, channels for obtaining lossless audio have become diverse, mainly divided into three paths:

This is the most traditional and reliable method. Users can use professional software like iTunes or EAC to rip physical CDs into FLAC or ALAC formats.

• Advantages: Permanent ownership of files, no risk of platform removal, and complete compliance with copyright regulations for personal use.

• Limitations: Modern computer hardware has mostly removed optical drive configurations, requiring external devices, and the ripping process is time-consuming.

This is currently the most convenient solution. Platforms such as Apple Music, Tidal, KKBOX, and Amazon Music HD all provide services with lossless or even High-Resolution specifications. Note that Spotify's HiFi plan has not yet been fully rolled out as of now.

Users pursuing ultimate sound quality can purchase and download high-resolution lossless files from professional music websites like HDtracks. Additionally, relevant resources can be obtained through precise keyword searches, though one must be mindful of copyright legality.

The necessity of pursuing lossless audio depends on the user's auditory discrimination ability and hardware budget.

Audio systems follow the "weakest link" principle (or Bucket Effect): the final listening experience depends on the weakest link in the signal chain. If playing a 24-bit / 192 kHz high-resolution file but using an adapter cable included with a phone and entry-level headphones, the advantages of lossless audio will be drastically reduced at the output end.

It is suggested that users refer to the hearing test provided by NPR for self-assessment. If one cannot significantly distinguish the difference between MP3 and WAV in a blind test, it may not be necessary to invest a large budget in upgrading equipment.

Insufficient Bluetooth transmission bandwidth is the main technical limitation for wireless listening to lossless audio currently. Although the playback source displays a lossless format, the audio often undergoes destructive compression during transmission to Bluetooth headphones.

The bandwidth of traditional Bluetooth protocols cannot carry the 1411 kbps data stream required for CD quality, so the audio must be encoded and compressed before transmission. This means that the signal received through Bluetooth headphones is essentially still a "lossy" version.

However, related coding technologies continue to evolve:

• aptX HD / Adaptive: Provides sound quality superior to traditional Bluetooth, with a listening experience close to lossless.

• Sony LDAC: Transmission rates can reach 990 kbps, extremely close to lossless specifications, and currently has a high penetration rate.

Outlook for Lossless Transmission: Qualcomm's aptX Lossless and MQA's SCL6 technology both claim to break through bandwidth limitations and achieve bit-to-bit true lossless transmission. However, this technology requires hardware support on both the transmitting end (phone) and the receiving end (headphones), and compatible products on the market are still few.

AirPlay transmits via Wi-Fi, and its bandwidth is significantly superior to Bluetooth, theoretically possessing the capability to transmit lossless audio. The AirPlay 2 protocol supports lossless transmission up to 16-bit / 44.1 kHz.

Although some tests indicate that when using Apple Music via AirPlay, the system middleware might transcode from ALAC to AAC in certain situations, overall, AirPlay can usually faithfully restore CD quality when playing local lossless files.

Compared to Bluetooth, AirPlay remains a relatively stable solution for wireless transmission of lossless audio. It is reported that Apple also continues to optimize related software architectures to ensure path integrity for streaming playback.

For users hoping to improve sound quality but unwilling to delve into complex cabling, Digital-to-Analog Converters, and amplifier configurations, selecting an integrated audio system with high-specification transmission capabilities is a viable path.

For example, integrated audio systems like the DUET MK3 that support AirPlay can connect directly to an iPhone via AirPlay without relying on third-party apps. Utilizing the high-bandwidth advantage of Wi-Fi bypasses the compression limits of Bluetooth, thereby releasing the potential of lossless audio.

The following is a compilation of common questions regarding lossless audio and playback equipment:

A1: This is usually due to transmission bottlenecks. The transmission rate of most Bluetooth codecs (like SBC, AAC) is far lower than the requirements of lossless audio, so the phone performs destructive compression on the audio before sending it. To experience true lossless, it is recommended to use a wired connection or equipment supporting Wi-Fi transmission (like AirPlay).

A2: Yes, the difference is massive. A standard CD-quality lossless song file is about 3 to 5 times larger than an MP3; if it is High-Resolution Audio, the size can be more than 10 times larger. If you do not have an unlimited mobile data plan, it is recommended to download over Wi-Fi first.

A3: Not necessarily. The file format is just a container; the content depends on the source. If an MP3 is converted to FLAC, although the format displays as lossless, the original lost audio details cannot be recovered out of thin air. Such files are called "fake lossless." True lossless must be ripped directly from the original master tape or CD.

A4: This is a controversial topic. In academic blind tests, untrained listeners often find it difficult to distinguish. However, for trained sound engineers or audiophiles, provided they have high-end playback equipment and an extremely low-noise environment, the difference in "airiness" and micro-dynamics brought by High-Resolution Audio can be perceived.