Advanced Audio Coding (AAC) is an aural bit stream compression technique that has supplanted other popular, yet older compression algorithms like MP3, and to date, it appears to be the best lossy audio compression standard. Here, we discuss in detail the Advanced Audio Coding (AAC) pros and cons.
Advanced Audio Coding AAC Pros and Cons: Introduction
Whether AAC fits your application depends on many factors which we weigh against each other herein. That is, for a given bit rate, you’ll experience the highest quality sound from AAC. Indeed, it features excellent sound fidelity while achieving data compression ratios of as much as 10:1.
Further, AAC makes possible the fitting of an entire music library of tens of thousands of songs into today’s portable media player devices. These sound virtually as crystal clear as uncompressed WAV PCM streams. They almost sound just like the clear audio that you find on compact discs.
Advanced Audio Coding AAC Pros and Cons: The Benefits, Advantages, and Pros
While by no means lossless, particularly at lower bit rates, AAC nonetheless, provides a virtually transparent encoding / decoding audio compression mechanism. Indeed, AAC facilitates rapid loading and playing of AAC compressed audio files very quickly. This means that AAC is an excellent stop-gap measure for storing very decent quality recordings of your music library. Until hard disks, flash memory, become cheap enough and eliminate the need to compress your audio files, AAC is the way to go, for the following reasons.
More Devices Understand AAC Today
Most smart phones like recent Nokia and Apple iPhone models, as well as the Windows, Android, and iOS-based tablet computers know how to play AAC and AAC+ audio files and streams these days. The same is true of popular portable media players such as the Sony Walkman, Apple iPod, Creative Zen, and Samsung Galaxy Player models. Fortunately, though the ubiquity of the previous (MP3) standard seriously slowed the progress from it into AAC during the first ten or fifteen years after they standardized AAC, current media players and computers are about as likely to offer AAC playing capabilities as they do MP3.
Smaller Encoded File Sizes
For a given sound quality level, AAC encoded files generally tend to be significantly smaller than MP3. This means that you can store more songs on that iPod.
A pretty mature compression system these days, the basic AAC standards layout was finalized in 1997. The players, devices, and codecs that implement AAC have become quite reliable over the past decade plus, and the compression system has become virtually ubiquitous among popular media players, smart phones, tablets, laptops, and desktop computers.
Better Sounding than MP3
Particularly at lower bit rates (below 64 Kbps), such as often used on speech and old-time radio show files, AAC provides significantly greater fidelity than MP3. Or, if less hard drive space consumed is more your thing than better fidelity, you can get the same MP3 fidelity you’re used to, but with a lower AAC bit rate. In fact, they wrote the AAC standard to overcome many of the known limitations of MP3.
Advanced Audio Coding AAC Pros and Cons: Short Decode Times
AAC has been optimized to require very little time (under half a second in most devices), to begin playing an audio file, though the decoding may require slightly more CPU while the file plays. Though it requires significantly more time to encode (to create the AAC file in the first place), these files start playing upon loading about as quickly as MP3 files.
Media player software, often free or very low cost, like iTunes, Winamp, and QuickTime, is capable of creating as well as playing AAC-encoded files on suitably provisioned computers.
Low Streaming Bandwidth
Not only does AAC produce smaller sized audio files for a given fidelity of sound, but it also cuts data rates in streaming audio applications such as Internet radio. Thus, with all else equal, AAC saves data costs when streaming to smart phones and tablets where the user is charged for the gigabyte of data received. For great sound with the least data usage, seek out those AAC audio streams.
AAC Less Lossy
AAC encoders and decoders, for a given bit rate, appear more aurally transparent than MP3; particularly for lower bit rate streams. However, even for 128 Kbps and higher bit rates, typical AAC encoders produce files that sound crisper and more full than what you can achieve with typical MP3 encoders.
Advanced Audio Coding AAC Pros and Cons: Better High Frequency Response
According to Wikipedia (see the links below), Advanced Audio Coding better “handles” audio frequencies of 16 KHz and higher. We’ve found in our tests using audio spectrometers, that AAC decoders reproduce more of these frequencies, with greater loudness, crispness, and clarity than MP3; particularly at lower decoding bit rates.
Native Variable Bit rate (VBR) Support
How AAC implements VBR is part of the AAC standard. VBR was less well-defined in the MP3 standard, and some dispute that MP3 officially supports VBR at all in the standard. So it’s been reported that some players that were supposed to be able to play MP3 files, could not play some variations of MP3 VBR files. Since how VBR is to be accomplished in AAC is clearly laid out, this problem is likely to happen less often among various AAC media players.
Wide Device Compatibility
The various “flavors” of AAC implementations generally tend to be compatible with one another, so long as the AAC standards version is the same. That is, an AAC file encoded with the Apple QuickTime AAC encoder will play on virtually any other device or app that supports AAC, such as Winamp, Windows Media Player, et al.
Large Range of Encoding Options
Bit rates (up to 320 Kbps). Sampling rates (up to 96 KHz). Number of audio channels (up to 48). Encoding quality levels (minimal, good, better, and best). All these choices highlight AAC’s many encoding options.
Advanced Audio Coding AAC Pros and Cons: The Problems, Concerns, Limitations, and Cons
Takes Significant Time to Encode
A typical four-minute stereo WAV file can take up to ten seconds to convert to AAC. So a batch of several thousand files, as we often convert as DJs, can require more than a whole day.
High CPU Utilization During Encoding
We do lots of batch WAV file conversions to AAC here, using either Winamp or Apple’s QuickTime player. During conversion, QuickTime produces a sustained 100 percent CPU utilization throughout virtually the entire encoding time per file. We’ve observed similar behavior in the Winamp encoder.
Advanced Audio Coding AAC Pros and Cons: Slightly Higher CPU Utilization During Decoding
Since the compression techniques are more complicated with AAC, generally speaking, it takes a bit more processor work to decompress the audio data while playing. This can result in slightly faster battery draining on mobile devices while streaming AAC, than while playing similar bit rate MP3 streams. However, this overhead is VERY small and thus, may not be noticeable with today’s ultra fast mobile processors and higher capacity batteries. Plus, a device with built-in native AAC hardware support may experience little or no increase of internal resources usage.
More Complicated File Organization
Typical AAC files utilize the MP4 container file organization standard, which contains size fields of the various regions within the file (boxes). These length fields, if incorrectly calculated by the encoder or corrupted by subsequent file copying or media device failure, can render the entire file unplayable. MP3 however, is more tolerant of these problems, because it relies much less on such size fields to find the audio data.
Less, but STILL Lossy
Though quite transparent, AAC is still not a completely lossless compression algorithm. It still throws away some audio components from the original recording that it deems as “irrelevant.” However, unless you have a top-grade sound card along with top grade headphones and headphone amplifier, you’ll be hard pressed to perceive these losses when comparing the original recordings to their AAC-encoded versions.
Advanced Audio Coding AAC Pros and Cons: Less Hardware Support
While AAC has become available on most of the popular media player platforms today, you still may encounter hardware / firmware / software, particularly in older devices, that do not support it. Tip: If you’re planning on buying a new media player, and you want it to play AAC files, be sure that the model you’ve selected can actually play the files and properly display your file tags, BEFORE you buy it. Fortunately, this problem either has, or is quickly morphing into a non issue due to the high degree of vendor support and embrace that the AAC standards have received in the 21st century so far. So eventually, you will be able to buy a device knowing that it will indeed play AAC.
Not much Sound Improvement on Higher Bit Rate Audio Streams
For example, 256 Kbps (and higher) MP3 streams seem to sound and measure about as well as 256 Kbps (and higher) AAC streams. So if you play higher bit rate streams, you might be better off sticking with MP3, for the moment anyhow. Given the greater hardware support for MP3 along with MP3’s lower CPU and battery utilization, MP3 may be a better choice at present. But AAC improvements really shine on lower bit rate audio (below 192 Kbps).
File Tagging Not Always Compatible Across Devices
For example, you may tag your AAC files (M4a) in Winamp. But the tags might not correctly display when you pull up those files on an IPod or Creative Zen. We’ve encountered no problems with this personally, though others reported it several years ago. Again however, we expect these anomalies to be corrected as universal device support and AAC ubiquity increase over time.
Lots of Different File Extensions
AAC can appear in files with the following extensions. .3gp, .aac, .m4a, .m4p, and .mp4 among others. But MP3 files feature just one extension: .mp3. The plethora of AAC extension can create support questions and problems on the various media player devices. Not all of these extensions are supported on all devices, even when the device itself contains the hardware and software to play AAC streams. The file extension may be the only factor that prevents playing the file, even when the player could otherwise play the data.
Advanced Audio Coding AAC Pros and Cons: MP3 Still More ”Standard” than AAC
MP3 is still universally available and works well in every device we’ve ever tested that claims to support it. AAC on the other hand, while more advanced, better sounding, and memory saving, may not always play on every device you’re likely to encounter. Further, MP3 will likely remain a mainstay for decades to come, since there are simply too many MP3 files out there to convert practically, if anyone would want to convert them at all. Why wouldn’t they? Because with lossy compression systems, you slightly degrade the file’s audio fidelity when you convert it. With each generation of conversions, the sound quality loss worsens. So people may not wish to incur that loss in their audio files just to get them into AAC.
AAC Encoding from Lossless Original Files May Be Too Costly
Plus, even if folks still had the first-generation lossless files (WAV, FLAC, AIFF, et al), so they could avoid these cumulative losses of repeated conversion (second, third,… generations of conversion), they might not be able to devote the months of time and computer resources required to transcode thousands of recordings, originally converted to MP3, into AAC. To get the original quality recording in order to make a first generation conversion to AAC, might require re-ripping their CDs or downloading them again from online music providers, and perhaps paying for some of them again as well. Thus, some of these files will remain MP3 for the foreseeable future, and so, we expect virtually every media player device to support MP3 for the rest of this generation’s life and beyond.
Advanced Audio Coding AAC Pros and Cons: Conclusion
But if industry keeps pushing for and improving AAC performance, the world will probably adopt it. Indeed, AAC will likely grow as ubiquitous as MP3 has. Indeed, as the public realizes the superior audio transparency, compatibility, and flexibility of AAC, AAC will play well everywhere, just like MP3.
Plus, once the technology improves enough, its “lossiness” will decrease to very low, unheard levels. Then, more people may decide to convert their MP3 files to AAC. Even if they no longer have the original lossless files, they still might convert. They may feel that the space savings is worth the slight loss in fidelity of a second generation conversion.
So far though, we see this as an sadly slow, yet inevitable progression. Thus, to those who create audio files, we suggest encoding them with AAC. Why? Because AAC is likely going to be the de facto compression standard in the next decade or two.
But hold on to your existing MP3 files a while longer. Support for them on popular media players and software isn’t going away soon. Keeping your first generation encoded files is important, especially if you no longer have access to the lossless original versions. The good news is that multi-generation file conversions won’t be as lossy in the future. So defer this conversion directly from MP3 as long as you can. For all first-generation conversions from lossless to AAC, AAC is at least as good as MP3. It’s much better than MP3 at lower bit rates.
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References for Advanced Audio Coding AAC Pros and Cons
- AAC Processor Utilization on Hydrogen Audio
- Advanced Audio Coding (AAC) on Wikipedia
- MP4 (MPEG-4) File Container Format on Wikipedia
- Where to buy AAC Media Players
Revision History for Advanced Audio Coding AAC Pros and Cons
- 2019-04-18; Added tags.
- 2019-02-17: Shortened many sentences.
- 2019-01-22: Updated page formatting and adjusted key phrase targeting.
- 2015-10-22: Added appropriate tags.
- 2015-10-01: Added appropriate tags.
- 2015-08-23: Originally published.