Can You Hear The Difference Between MP3 And AAC?

Lossy file formats like MP3 and AAC share the convenient characteristics of taking up minimal storage space and being compatible with most devices. But can you hear a difference between them?

It is possible to hear the difference between AAC and MP3 files, though the distinction between these coding formats is barely audible (especially at higher bit rates).  AAC files use a superior compression algorithm to MP3s, which enables more efficient and accurate coding of audio information

The codec one uses for recording, storing, or sharing digital audio is crucial because it influences sound quality. In the case of MP3 and AAC files, this difference is worth considering. The following technical insights should help readers appreciate why AAC and MP3 file formats sound slightly different.ย 

MP3, AAC, And Their Subtle Sound Quality Differences

MPEG Layer 3 (MP3) and Advanced Audio Coding (AAC) files sound remarkably similar because of their shared coding lineage.  Both digital formats use lossy compression to encode audio information.

Lossy data compression employs algorithms to remove the lowest and highest frequencies from the source audio signals. The removal of these virtually imperceptible frequencies is called perceptual coding. 

Audio data that remains after perceptual coding gets translated into a new, compressed file that is smaller (has fewer bits) than the original recording.

While some of the original audio information gets lost in this process, lossy compression has several benefits over other forms of audio conversion.

AAC and MP3 formats have the benefit of requiring minimal storage space, and they are quicker and easier to share than the original audio data. At the same, AACs and MP3s have a high level of sound quality that accurately recreates the information from the source recording.

The following table summarizes a few of the crucial technical features and characteristics of AAC and MP3 codecs.

Codec Feature MP3 AAC
Algorithm MDCT-fFT hybrid MDCT
Channels 2 (MPEG-1)  6 (MPEG-2 surround sound) up to 48
Sample rate (range) 16kHz to 48kHz 8kHz to 96kHz
Compression efficiency tools No Yes
Joint stereo Unable to isolate individual frequency bands Able to isolate individual frequency bands

Comparing The Sound Quality Of MP3 and AAC

The audio quality of AAC and MP3 files is very similar, but it is not identical.

In general, the AAC format sounds superior to MP3s, although most people would not hear the difference. The difference in the sound quality of AAC and MP3 codecs is most apparent at low bit rates. This superiority makes sense when considering the AAC is a newer, more advanced digital audio coding format than MP3.

Results from standardized double-blind listening tests with trained participants demonstrate that the AAC format produces a higher sound quality than MP3 files. These tests compare identical audio data encoded at the same bit rate via AAC and MP3 formats.

Participants of these double-blind tests report that AAC has a slightly brighter and cleaner sound than the MP3 format.

When converting data at the same bit rate, there is a subtle difference in sound quality between AAC and MP3 files. International standards for audio encoders are meant to ensure there is no audible difference between formats like MP3 and AAC

As a result, the average person might struggle to hear the difference between an AAC and MP3 file. Without equipment like a signal-to-noise meter, one needs a well-trained ear to distinguish between the sounds of MP3 and AAC recordings.

Why Do AAC and MP3 Sound Slightly Different?

AAC is a newer and more advanced iteration of the MP3 audio encoder. Subtle differences between the sound of AAC and MP3 are due to this progression in coding design and capabilities.

The principal reason why AAC and MP3 sound slightly distinct from one another is that they do not use the same compression algorithms.

AAC employs an audio coding algorithm called modified discrete cosine transform (MDCT for short). This algorithm is newer and more technologically advanced than the one used for the MP3 format.

In contrast to the AAC codec, MP3 has of a hybrid between MDCT and fast Fourier Transform (FFT) algorithms. This coding combination is less efficient than the pure MDCT algorithm that AAC uses.

AAC also has additional audio coding capabilities that contribute to the subtle but measurable difference in sound quality between this codec and MP3.

Significance Of Bit Rates When Comparing MP3 And AAC

It is crucial to emphasize that the difference in the audio quality of MP3 and AAC codecs is least noticeable when converting audio data at high bit rates.

The distinction between AAC and MP3 becomes more audible with lower bit rate conversions (below 128kps), which reveal AACโ€™s superior audio quality.

Audio Coding Advantages Of AAC Vs MP3

The improved audio coding of AAC gives this format several advantages over MP3. While MP3 is compatible with a more comprehensive range of audio processing hardware and software, AAC generally produces a higher-quality sound.

It is examining the advantages of AAC to understand how the codec generally produces superior audio quality compared with the MP3 format.

Enhanced Coding Of Audio Data

Due to its compression algorithm and modular coding, AAC codes audio data more efficiently and accurately than MP3 encoders.

As a result, AAC coding creates smaller files than the MP3 format. The AAC codec also produces a higher fidelity compression of audio data when compared with MP3. 

Expansive Sample Rate Range

The AAC format also enables the encoding of a wider range of sample rates. AAC coding processes sample rates from 8kHz to 96kHz (for 1 to 48 channels), while MP3 is limited to the 16kHz to 48 kHz range.

Removing Spectral Leakage

Recording or converting audio information with AAC allows for the removal of spectral leakage (when signals with a single tone overlap across multiple frequencies).

The AAC format is compatible with the Keiser-Bessel window function, making it possible to cut spectral leakage out from the original audio signals.

More Versatile Joint Stereo Encoding

Another advantage of AAC is that it offers greater versatility than MP3 when encoding audio in joint stereo,(combining left and right channels for compression efficiency while retaining stereo).

AAC allows joint stereo mode to be applied to individual frequency bands, making the conversion process more controlled.

The MP3 codec, in contrast, applies joint stereo mode to every frequency band simultaneously. MP3 performs this combined stereo encoding with a frame-to-frame method, and it does not allow for the isolation of specific bands

Extra Modules To Enhance Compression Efficiency

There are numerous sophisticated tools (or modules) available for AAC encoders. These tools boost the efficiency of audio data compression and are not available for use with MP3.

The compression-enhancing tools that are available as standard features with the AAC format include:

  • backward prediction,
  • perceptual noise substitution,
  • temporal noise shaping,
  • error resilience.

These tools are not available for use with MP3, giving AAC a considerable advantage when compressing audio data.

Better Processing Of High-End Frequencies

The AAC digital audio coding format is more effective than MP3 at processing signals at the high-end of the frequency spectrum.

AAC encoders can encode frequencies higher than 16kHz more accurately than MP3 codecs. This improved capability means high frequencies typically sound better in AAC than in MP3 format.

More Channels

This channel capability is significantly more expansive than the MP3 codec. MP3 encoders work with 2 channels in MPEG-1 mode. In MPEG-2 surround sound, MP3 can convert a maximum of 6 channels.

Conclusion

The sound quality of AAC and MP3 files is virtually the same, though attentive and discerning listeners can hear a subtle difference between these lossy formats. While both audio coding formats produce lossy compressed files efficiently, AAC has a cleaner and more high-fidelity sound than the MP3 codec.

The principal reason for this difference is due to the more sophisticated MDCT algorithm that AAC uses to convert source audio information more accurately and efficiently than MP3. AAC also has several advantages over the older MP3 format, including an array of compression-enhancing software tools.

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