Clarification of MPEG 4, AAC and Apple

Based on posts/responses on the forums, it appears there is still a significant amount of confusion regarding audio codecs and their implications.

For clarification purposes, "MP3" is officially known as MPEG-1 Layer 3. This audio codec provides the popular compression format that both iTunes and the iPod support.

Songs can be encoded at varying "bitrates". The most common bitrate for MP3 is probably "128kbps". This translates into 128 kilobits per second -- which means the format will use 128kilobits of data to encode one second of audio - no more, no less. Therefore, the final size of a file depends on both Bitrate and the Length of the Song.

Many users, however, prefer to utilize larger bitrates to achieve higher quality audio, but at the sacrifice of a larger final file size. Based on this popularly referenced c't magazine blinded study, it is commonly held that 256kbps MP3s are equivalent to original CD Audio:


    In plain language, this means that our musically trained test listeners could reliably distinguish the poorer quality MP3s at 128 kbps quite accurately from either of the other higher-quality samples. But when deciding between 256 kbps encoded MP3s and the original CD, no difference could be determined, on average, for all the pieces. The testers took the 256 kbps samples for the CD just as often as they took the original CD samples themselves.

AAC/MPEG4

This page at Apple helps clarify some terms and definitions regarding the audio format: AAC. Advanced Audio Coding (AAC) is the audio codec for the standard known as MPEG-4. According to Apple's site, AAC provides multiple advantages over MP3 -- but the most significant for end-users is the improved compression algorithm:


    AAC compressed audio at 128 kbps (stereo) has been judged by expert listeners to be "indistinguishable" from the original uncompressed audio source.*

As a result, the advantage of AAC will be better quality audio at the same file sizes. Or, alternatively, equal or better quality at smaller sizes.

Some commonly asked questions:

Q: Is a 128kbps AAC/MPEG4 file smaller than a 128kbps MP3?

A: No. They are exactly the same size... but the AAC file should sound better. See above.

Q: Will there be a way to convert my MP3's to AAC files?

A: Converting directly from MP3 to AAC is not recommended (by this author). Going from a 128kbps MP3 to a 128kbps AAC file will provide no space spavings, and yet you will likely lose audio quality. (both are "lossy" file formats). Remember, you will never "regain" the quality lost when a song was encoded into MP3. The recommended course of action would be to re-rip the files from its original format (CD, for example).

Related Forum: Mac Apps

Popular Stories

iPhone SE 4 Thumb 1

iPhone SE 4 With Apple's Own 5G Modem 'Confirmed' to Launch in March

Tuesday November 19, 2024 12:12 pm PST by
Barclays analyst Tom O'Malley and his colleagues recently traveled to Asia to meet with various electronics manufacturers and suppliers. In a research note this week, outlining key takeaways from the trip, the analysts said they have "confirmed" that a fourth-generation iPhone SE with an Apple-designed 5G modem is slated to launch towards the end of the first quarter next year. In line with previo...
airtag purple

AirTag 2 Rumored to Launch Next Year With These New Features

Sunday November 17, 2024 5:18 am PST by
Apple released the AirTag in April 2021, so it is now three over and a half years old. While the AirTag has not received any hardware updates since then, a new version of the item tracking accessory is rumored to be in development. Below, we recap rumors about a second-generation AirTag. Timing Apple is aiming to release a new AirTag in mid-2025, according to Bloomberg's Mark Gurman....
Magic Mouse Next to Keyboard

No, Apple CEO Tim Cook Didn't Say He Prefers Logitech's MX Master 3 Over the Magic Mouse

Sunday November 17, 2024 3:03 pm PST by
While the Logitech MX Master 3 is a terrific mouse for the Mac, reports claiming that Apple CEO Tim Cook prefers that mouse over the Magic Mouse are false. The Wall Street Journal last month published an interview with Cook, in which he said he uses every Apple product every day. Soon after, The Verge's Wes Davis attempted to replicate using every Apple product in a single day. During that...
Generic iOS 18 Feature Real Mock

Apple Releases iOS 18.1.1 and iPadOS 18.1.1 With Security Fixes

Tuesday November 19, 2024 10:10 am PST by
Apple today released iOS 18.1.1 and iPadOS 18.1.1, minor updates to the iOS 18 and iPadOS 18 operating systems that debuted earlier in September. iOS 18.1.1 and iPadOS 18.1.1 come three weeks after the launch of iOS 18.1. The new software can be downloaded on eligible iPhones and iPads over-the-air by going to Settings > General > Software Update. Apple has also released iOS 17.7.2 for...
at t turbo indicator iphone 16 pro max v0 8hrh7w5f3w1e1

AT&T Turbo Indicator Showing Up in iPhone Status Bar for Subscribers

Wednesday November 20, 2024 3:42 am PST by
AT&T has begun displaying "Turbo" in the iPhone carrier label for customers subscribed to its premium network prioritization service, according to reports on Reddit. The new indicator seems to have started appearing after users updated to iOS 18.1.1, but that could be just coincidence. Image credit: Reddit user No_Highlight7476 The Turbo feature provides enhanced network performance through ...
iPhone 17 Slim Feature Single Camera 1 Redux

'iPhone 17 Air' Rumored to Surpass iPhone 6 as Thinnest iPhone Ever

Monday November 18, 2024 1:07 pm PST by
In a research note with Hong Kong-based investment bank Haitong today, obtained by MacRumors, Apple analyst Jeff Pu said he agrees with a recent rumor claiming that the so-called "iPhone 17 Air" will be around 6mm thick. "We agreed with the recent chatter of an 6mm thickness ultra-slim design of the iPhone 17 Slim model," he wrote. If that measurement proves to be accurate, there would be ...
bug security vulnerability issue fix larry

Make Sure to Update: iOS 18.1.1 and macOS Sequoia 15.1.1 Fix Actively Exploited Vulnerabilities

Tuesday November 19, 2024 10:52 am PST by
The iOS 18.1.1, iPadOS 18.1.1, and macOS Sequoia 15.1.1 updates that Apple released today address JavaScriptCore and WebKit vulnerabilities that Apple says have been actively exploited on some devices. With the JavaScriptCore vulnerability, processing maliciously crafted web content could lead to arbitrary code execution. The WebKit vulnerability had the same issue with maliciously crafted...