Which Is The Highest Quality Audio Format?

With the expansive variety of digital audio formats available today, it can be tricky to know which is best. So, which audio format has the highest quality?

The highest-quality audio format is PCM (pulse code modulation). PCM is a high-resolution, uncompressed analog-to-digital sampling format that reproduces every amplitude and frequency present in the input audio signal. Audio in the PCM format is usually stored in container files like WAV and AIFF.

Understanding PCM and the container formats that store this uncompressed audio is crucial for anyone serious about maximizing sound quality. The following elucidation of PCM audio is worth perusing for individuals on a mission for exceptional audio quality. 

PCM Is The Highest Quality Audio Format

Pulse code modulation (PCM) is an uncompressed audio format offering the highest sound quality. This uncompressed audio is typically stored in the WAV or AIFF container formats.

The fundamental reason PCM (and its container formats) produce such superior sound quality is that they record or transfer input audio information in its entirety. Uncompressed audio files replicate the sound of the original audio with total fidelity, reproducing the full dynamic range and tonal subtleties present in the input audio information.

Uncompressed formats stand in juxtaposition to compressed audio. Lossy and lossless compression formats remove and manipulate input audio data to create smaller files. As a result, their sound quality is technically inferior to uncompressed formats such as WAV or AIFF, especially in the case of lossy formats like MP3.

While uncompressed audio formats have higher sound quality, it is worth emphasizing that compressed audio can also sound excellent. Aside from audiophiles, musicians, and sound engineers, most people won’t hear a dramatic difference between uncompressed and compressed formats (unless the latter have low bit rates).

Before proceeding, it is necessary to clarify the term format. This term is often used loosely to refer to multiple distinct elements of audio conversion and storage, such as codecs, containers, and data types.

So, the PCM format is the name of a technique for sampling analog signals. The name also refers to the resulting digital information created or represented through the PCM technique.

In contrast, WAV and AIFF are container formats that store audio data (but do not sample it). WAV and AIFF containers usually hold PCM data, so they are conventionally called uncompressed formats (despite also being capable of storing compressed audio).

PCM and its primary associated containers are described below, enabling readers to understand how these formats operate and why they produce high-quality audio.

PCM

Pulse-code modulation (PCM) refers to a technique for processing analog sound signals into a digital form. PCM also refers to the audio data that gets produced through this method. Data in the PCM format is typically found on compact discs (CDs) but is also for applications like video production and telephone communication.

A defining characteristic of PCM is that is an uncompressed format. As such, PCM data provides a complete, high-fidelity representation of the original analog signal.

PCM Sampling Method

The PCM method captures analog audio by sampling the waveform’s amplitude at equidistant intervals. Every sample undergoes quantization, which transforms the continuously varying analog sine waveform into a digital form consisting of a limited number of numerical values.

In the PCM quantization process, each sample of the analog signal is assigned the closest available binary value (determined according to the specified bit depth).

A prevalent sub-type of PCM often used on compact discs is called linear pulse-code modulation (LPCM). LPCM uses a slightly different quantization technique than PCM when processing analog signals. The LPCM method applies uniform quantization along the length (linearly) of the analog waveform.

Sampling Rate And Bit Depth Of PCM

The bit depth and sampling rate parameters determine the resolution or fidelity of the resulting PCM audio representation.

As a result, higher bit depths and sampling rates also generally equate to increases in the quality of PCM audio (though exceeding a certain maximum threshold delivers no audible improvements in sound quality). PCM samples at two to more times the frequency of the input analog signal.

The standard sampling frequency (number of samples created in a given time) for PCM audio is 44.1kHz. PCM audio on DVDs has higher sampling frequencies that range from:

  • 44.1kHz,
  • 48kHz,
  • 88.2kHz,
  • 176.4kHz,
  • 192kHz.

The PCM audio format processes analog signals at the following bit depths (number of bits in each sample):

  • 8 bits (not supported on DVD),
  • 16 bits (the standard for CDs),
  • 20 bits,
  • 24 bits.

PCM Data Storage

PCM audio data generally gets stored in two ways. The first way is as raw data, which is uncompressed
and does not get stored in a container file with accessory header information. Raw PCM data is held in files with the .pcm, .sam, or .raw file name extensions.

The second and more common way to store PCM audio data is by encoding it in container files like WAV and AIFF and AU. These formats produce sound quality virtually indistinguishable from the PCM data they typically contain.

WAV

Waveform Audio File Format (WAV) is a container file format (sometimes called a wrapper). Windows OS employs WAV as the primary container for storing uncompressed audio information.

Though WAV can hold compressed audio, it is generally categorized as an uncompressed format because it usually contains PCM data.

WAV is one of several sub-types of the Resource Interchange File Format (RIFF). RIFF is a tagged container file structure rather than format and stores audio data in elemental components called chunks.

Individual RIFF chunks have tags, which are codes consisting of four characters that indicate information such as:

  • file size,
  • sampling frequency,
  • bits assigned to each channel,
  • metadata.

As WAV is principally a container that stores uncompressed audio, it is known for its sound quality. For this reason, WAV is used widely in professional audio production and editing.

The quality of WAV comes at the cost of file size. Uncompressed WAV files are bulky due to the considerable amount of data they contain, so they have significant bandwidth and data storage requirements. Consequently, WAV is ill-suited for sharing and storing, particularly compared to compressed formats like MP3.

AIFF

Audio Interchange File Format (AIFF) is a container format that Apple Inc. first released in 1988. AIFF is specially designed for Macintosh computers but also plays on Windows Media Player. 

Like WAV, AIFF is most frequently used to store uncompressed PCM audio data, so this format from Apple produces equally high sound quality.

There is also a less common version of the format called AIFF-C, which holds compressed audio.

AIFF encodes audio in tagged chunks but uses the IFF container file structure. IFF is the big-endian predecessor of RIFF (whose byte sequence was adjusted to little-endian to achieve compatibility with Intel’s x86 microprocessor).

There are multiple kinds of chunks in an AIFF audio file. The two essential chunks are the:

  • Common Chunk,
  • Sound Data Chunk.

Non-essential chunks in AIFF files include:

  • Audio Recording Chunk,
  • MIDI Data Chunk,
  • Instrument Chunk,
  • Marker Chunk,
  • Application Specific Chunk.

AU   

Au is a less complex container file format than WAV and AIFF that also stores and plays back PCM audio.

Released by Sun Microsystems, Au stores audio data encoded in various formats. Au files usually contain μ-law logarithmic-encoded audio but also hold multiple varieties of PCM data, including LPCM and Adaptive Differential PCM (ADPCM).

The Au container format faithfully reproduces the high-resolution sound quality of PCM audio data.

The bit depth of Au files with PCM audio spans from 8-bit to 32-bit. Typical sampling rates for Au range from 8kHz all the way up to 48kHz.

Comparing The Quality of PCM And Its Containers Formats

So, PCM is the highest quality audio format due to its uncompressed form. The superior quality of PCM is also matched by the container formats like WAV, AIFF, and Au that store this kind of uncompressed audio.

However, comparing the quality of different audio formats is a complex endeavor involving countless complicating factors.

While the sound quality of PCM audio is superior to compressed formats, this difference is often mathematical rather than practical.

Human hearing limitations and technologically-advanced compression codecs mean that quality differences between PCM and compressed formats are often too subtle for most listeners to perceive.

The Limits And Variability Of Human Hearing

The first point to emphasize is that the average human auditory system cannot detect sounds below 20Hz and above 20kHz. Yet, many differences in the sound of uncompressed and compressed formats fall outside this frequency range, making these distinctions inaudible to humans.

There is also a limit to the amplitude human ears can tolerate. People can perceive sounds at volumes in a dynamic range of 0dB to about 120dB (the range is less for the lower and higher frequencies). Amplitudes above this limit can cause physical discomfort and pain to a listener’s auditory apparatus.

However, listening at these intolerably loud volumes would be necessary to hear many of the most obvious differences between PCM and compressed formats. This is because noise artifacts that compressed formats introduce only become audible at excessively high amplitudes.

In other words, one is unlikely to listen to audio at volumes far exceeding the maximum threshold, so one won’t have a chance to detect some of the conspicuous sound quality differences between PCM and compressed formats.

Ear training also has a significant influence on a listener’s ability to discern deviations between the quality of uncompressed and compressed audio. Musicians, sound engineers, and audiophiles might notice differences that elude the average listener’s ear.

The age of the listener also affects their ability to accurately and reliably compare audio formats. For example, a person’s capacity to hear sounds at the high end of the frequency spectrum generally diminishes. Younger individuals can usually perceive subtle deviations in the quality of different audio formats.

Audio Hardware

Audio hardware is another complicating variable that affects a person’s ability to discriminate between the quality of PCM and other audio formats. Crucial audio hardware elements that influence the sound quality of a digital audio file include:

  • amplifiers,
  • headphones or speakers,
  • cables,
  • computer sound cards.

High-quality hardware makes it easier to compare PCM and uncompressed formats because one can hear the subtle nuances in the audio. For example, the quality difference between a highly-compressed MP3 and a PCM-containing WAV file is more conspicuous when listening through professional headphones.

Audio format comparisons are considerably more challenging when using hardware that is damaged, poorly designed, cheaply manufactured, or has limited performance capabilities. Low-quality audio hardware potentially reduces audio clarity, introduces noises, and makes the lowest and highest frequencies inaudible.

For instance, it would require nearly superhuman hearing powers to distinguish between audio formats if one were listening through the speakers of a cellphone from the early 2000s.

High-Performance Compression Formats

Advancements in compression encoding also complicate comparisons between PCM and compressed formats. These technological improvements to compressed formats make it more challenging to differentiate them from uncompressed PCM audio.

Lossy Compression

The quality of the first generations of lossy compression formats like MP3 was noticeably inferior to uncompressed audio, particularly to listeners with trained ears.

Lossy compression formats have, however, become increasingly effective at approximating source audio signals without compromising audio quality. The performance of current lossy formats makes it tricky to distinguish them from PCM audio.

Recent, improved lossy compression encoders like AAC and later versions of MP3 use enhanced perceptual coding to identify and remove inaudible (or inessential) sound components.

When encoded with an advanced codec at mid to high bit rates, lossy compression produces output sounds virtually identical to the original audio.

Lossless Compression

Lossless compression formats like FLAC and ALAC are widely accepted as having higher quality than their lossy cousins. Unlike lossy formats, lossless compression formats do not lose source audio information.

FLAC, ALAC, and related lossless formats use highly-efficient algorithms to compress source audio with no audible reduction in sound quality.

There is a negligible chance that listeners with untrained ears will hear the difference between lossless compressed and uncompressed audio formats. Even sound engineers and amateur audiophiles might struggle to differentiate between these lossless formats and WAV or AIFF files containing uncompressed PCM audio!

Volume control knob of hi-fi amplifier

Encoding Parameters: Bit Rates

The bit rate of an audio file indicates how much of the information it contains gets processed in a given period during playback. Bit rate is conventionally measured in kilobits per second (kbps), and is critical to consider when comparing the quality of different audio formats.

Bit rate affects sound quality because the resolution of the audio increases when a higher number of bits are available to represent the input sound signal. Consequently, the general rule is that increased bit rates produce higher-quality audio (the difference between higher bit rates is negligible).

The standard bit rate for PCM and its container formats like WAV and AIFF is 1411.2kbps (but it can go considerably higher). This commonly-applied bit rate for PCM derives from the bit depth (16 bits) multiplied by the sampling rate (44.1kHz) and the number of channels (2).

The bit rates for compressed audio formats vary more and are generally lower than uncompressed formats like PCM. In the case of MP3 lossy compressed files, the available bit rates range from 32kbps to 320kbps. Lossless formats like FLAC and ALAC encode at bit rates ranging from 400kbps to 1411kbps (standard for lossless).

Bit rates have the same effect on the quality of compressed formats (which range from 32kbps to 1411kbps). Decreasing the bit rate corresponds with a higher compression rate and more significant file size and quality reductions.

Conversely, increasing the bit rate setting decreases the level of compression applied to the input audio. The result is a larger file with higher quality sound than if one had used a low bit rate. 

PCM Vs Low And High Bit Rate Compressed Audio

Sound quality differences between PCM (including its container formats) and compressed audio are more or less conspicuous, depending on their bit rates.

Briefly put, when compressed files have low bit rates, it is easier to distinguish them from uncompressed PCM audio. Conversely, it is more difficult to hear the difference between high-bit-rate compressed audio and PCM.

Lossless compressed files sound indistinguishable from PCM when encoded at the conventional bit rate of 1411kbps.

The quality differences between high-bit-rate lossy formats and PCM are also negligible and might not be unnoticed by casual listeners with untrained ears.

If compressed audio files are encoded at low bit rates, they contrast more starkly with PCM (and its containers like WAV).

This effect is especially applicable to lossy compression formats. For instance, MP3 files encoded at bit rates of 96kbps or less will produce a noticeably inferior sound quality compared with PCM audio.

Conclusion

PCM has the most compelling claim to being the highest-quality audio format. This uncompressed digital format samples full analog signals without altering the original sound information. PCM audio is commonly stored in container formats like WAV, AIFF, and (to a lesser extent) Au.

The quality of PCM and its containers is higher than widely-used compression formats. The superior quality of PCM is easier to detect when compared with compressed formats that are encoded at low bit rates. At high bit rates, compressed formats sound almost indistinguishable from PCM audio.

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