AAC to MP3: Convert Audio from AAC(Advanced Audio Coding) to MP3(MPEG Layer-3) with River Past Audio Converter, AAC2MP3 converter, conversion

What is AAC?

AAC, Advanced Audio Coding, is a technique for compressing digital audio files. Officially part of the MPEG-4 standard, it is most widely used to create small digital audio files.

AAC is conceptually similar to the ubiquitous MP3 format. AAC is a lossy algorithm, meaning the original digital audio cannot be recreated from the compressed bits alone. In terms of audio fidelity, however, there is no loss of data if the compressed audio is properly encoded. AAC claims an advantage over MP3 in this regard: while MP3 requires a bit rate of approximately 256 kilobits per second (kbps) to achieve transparency, AAC can achieve the same quality at 128 kbps. This allows AAC files to be roughly half the size of MP3 files of the same quality, and one-tenth the size of CD digital data.

AAC provides several other advantages over MP3. It is capable of handling much higher and lower frequencies of sound, provides up to 48 channels of audio, and allows the creation of low-latency audio necessary for two-way communication.

There are two types of AAC files. The most common one is embedded in MPEG-4 container. Its file extension is usually m4a. The popular iTunes encode AAC audio in this format. You only need to have Apple QuickTime installed to decode these files.

A less common one is the plain AAC file, usually with .aac file extension. To convert from this type, you need to have DC-Bass Decoder installed.

What is MP3?

MP3 is a digital audio compression algorithm that acheives a compression factor of about twelve while preserving sound quality. It does this by optimising the compression according to the range of sound that people can actually hear. MP3 is currently (July 1999) the most powerful algorithm in a series of audio encoding standards developed under the sponsorship of the Moving Picture Experts Group (MPEG) and formalised by the International Organization for Standardization (ISO).

MP3 is very different from Layer 2, using an additional MDCT layer to increase frequency resolution. Its scale factor groups are more optimised for the human ear, and it uses nonlinear sample quantisation and Huffman coding. MP3 files (filename extension ".mp3") can be downloaded from many World-Wide Web sites and can be played using software available for most operating systems (also downloadable), e.g. Winamp for PC, MacAmp for Macintosh, and mpeg123 for Unix. MP3 files are usually downloaded completely before playing but streaming MP3 is also possible. A program called a "ripper" can be used to copy a selection from a music CD onto your hard disk and another program called an encoder can convert it to an MP3 file.

Windows ships with limited MP3 encoding support. The output sample rate is limited to 24khz and the bitrate is limited 56kbps. However, many add-on packages from open source community make it possible to encode at higher sample rate and bitrate.

A commonly used open source codec is LAME. LAME comes in different forms, including a ACM (Audio compression manager) codec and a DLL (lame_enc.dll). Caution: LAME ACM does not work well on many computers, regardless which software is loading it. It is best to avoid installing LAME ACM and use lame_enc.dll instead.

MPEG.ORG is an excellent source for additional information on MPEG format and usage.

When you encode MP3 audio, we recommend you to install lame_enc.dll.

Launch River Past Audio Converter

Once River Past Audio Converter is installed properly, launch Audio Converter.

Add File

Click on the "Add File" button on the tool bar. The standard file open dialog appears. Select "AAC - Advaned Audio Coding" in its "Files of type" combo box.

Note: To convert from AAC files, you must have DC-Bass Decoder installed.

River Past Audio Converter

Select output format

Use the setting panel on the bottom of the window to control the output format. Click on the toggle to the left of the "Format" label to expand the panel. Select "MP3 - MPEG Layer-3" as the "Audio Type".

You can change the sample rate, channel (stereo or mono) and bitrate.

Note: The standard MPEG Layer-3 audio compressor is limited to maximum 24khz and 56kbps. Please install Lame_enc.dll for higher sample rate and bitrate.