AAC to M4R
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| File extension | .aac |
|---|---|
| File category | Audio |
| Stands for | Advanced Audio Coding |
| Developer | Bell Labs, Fraunhofer IIS, Dolby Laboratories, LG Electronics, Sony Corporation (Combined Efforts) |
| Overview | AAC is the descendant of the MP3 format. It provides better sound quality using a similar bit rate as of MP3. Besides this, it uses lossy data compression but it has high standards of audio quality than of MP3. We can find this format on a number of platforms and Apple's iTunes is one such example that uses it as default audio format. Size of its file is much smaller which is approximately one-tenth of MP3 file. It also neglects the redundant information that is not even processed by the human ear and is often not noticed. Although, this format was introduced as MPEG-2 Part-7, yet, standardization was done by ISO/IEC as a part of the MPEG-2 and MPEG-4 families. It is also termed as MPEG-2 NBC (Non- Backward Compatible) because it is incompatible with MPEG-1 audio formats i.e. MP1, MP2, MP3. |
| Technical description | Modified discrete cosine transform(MDCT) algorithm is used by AAC which ensures that it provides high compression efficiency. MPEG-2 PART-7 has three default profiles namely Low Complexity (LC), Main Profile (Main) and Scalable Sample Rate (SSR). These profiles come with Perceptual Noise Substitution which enhances coding efficiency and provides excellent audio quality. Furthermore, it uses Auditory Masking to ignore the surplus information. This codec has come up with advanced features which are not available in the predecessor. These include additional sample rates ranging from 8 to 96 kHz, 48 Channels, better efficiency with a simpler filter bank, higher coding efficiency for stationary signals and higher coding accuracy for transient signals. |
| Links | wikipedia.org (opens in new tab - official documentation) |
| File extension | .m4r |
|---|---|
| File category | Audio |
| Stands for | MPEG-4 PART 14 for iPhone ringtones |
| Developer | Apple Inc. |
| Overview | M4R is one of the extensions of MPEG-4 Part-14 and it is specially designed by Apple for iPhone ringtones. It is just the relabelling of AAC and M4A. This extension provides an excellent quality of ringtones for iPhones and the size of the ringtone is also small. There are certain steps that one needs to follow for the conversion of any song into this format (iPhone ringtone). Firstly, select any song of 30 seconds and covert it to AAC format using iTunes. Then rename this file using .m4r extension. Finally, by using the iTunes transfer your ringtone file to iPhone. This can be done by connecting your iPhone to the computer and syncing the playlist. Now a user can easily use this ringtone for phone ring, alerts, alarms etc. It should be noted that these files will be supported only by the latest version. Hence, use the current version of iTunes. |
| Technical description | It uses a lossy compression algorithm to encode the ringtones that is same as AAC and MP3 eareensions. But it has the additional feature of auditory masking which means it neglects other sounds which can be detected or recognized while listening or hearing another sound. It only discards the information which is surplus for the human ear. This results in good quality of iPhone ringtones. It takes less storage space without affecting the quality of audio. It is also a segment of MPEG-4 standard and this is stated in the ISO-IEC standard 14495-3. |
| Links | wikipedia.org (opens in new tab - official documentation) |
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