AC3 to MP3: Convert Audio from AC3(Dolby Digital AC-3 Audio) to MP3(MPEG Layer-3) with River Past Audio Converter, AC32MP3 converter, conversion

What is AC3?

Dolby Digital, formerly known as AC-3, is a digital audio compression format. Dolby Digital takes advantage of how the human ear processes sound. When coding noise is close to the frequency of an audio signal, that audio signal masks the noise so that the human ear hears only the intended audio signal.

Dolby Digital is used with digital versatile discs (DVDs), in North America only. European DVD's use MPEG audio instead.

Dolby Digital provides five full-bandwidth channels, front left, front right, center, surround left, and surround right, for true surround sound quality. A low frequency effect (LFE) channel is included that provides the sound needed for special effects and action sequences in movies. The LFE channel is one-tenth of the bandwidth of the other channels and is sometimes erroneously called the subwoofer channel. This multichannel scheme is known as 5.1 channel.

To convert AC-3 audio to other formats in River Past software, please have AC-3 Decoder filter 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 "AC3 - Dolby Digital" in its "Files of type" combo box.

Select the file you want to convert and click "Open". The file will be added to the conversion file list.

Note: To convert from AC-3 files, you must have open source AC-3 decoder installed.

Once the AC-3 Decoder Filter is installed, you will also find a AC-3 Control Panel in your (Windows) Start | Settings | Control Panel area. It allows you to change the settings for the decoder. Often, you may find the default volume from the decoder is lower than desired and it is necessary to adjust the volume in this control panel.

If you cannot add the AC3 file, please verify your AC-3 Decoder filter installation.

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.