Introduction
A short article describing how to convert AMR audio files to MP3 with the Pazera Free Audio Extractor. This program is completely free, also for commercial use, and you can download it here.
AMR – Adaptive Multi-Rate (AMR-NB, AMR-WB i AMR-WB+)
AMR is a multimedia container and audio compression format optimized for encoding human speech in order to transmit coded signals in telecommunications networks. AMR compression is widely used in GSM and UMTS systems.
AMR compression is widely used in mobile phones – voice recorders built into these phones very often record audio in AMR format. In addition, the phones that allows to record movies usually store them in a 3GP files, in which the audio stream is mostly encoded using AMR compression.
There are several variants of AMR compression:
- AMR-NB (Adaptive Multi-Rate – Narrowband) – this is the basic and most commonly used method of AMR compression, which uses audio sampling frequency of 8 kHz, and bitrate 4.75, 5.15, 5.9, 6.7, 7.4, 7.95 , 10.2 or 12.2 kbit/s. Audio files with audio tracks encoded using this method of AMR compression usually have the extension .amr
- AMR-WB (Adaptive Multi-Rate – Wideband) – a newer version of AMR compression, which uses a 16 kHz of sound sampling and bitrates equal to 6.6, 8.85, 12.65, 14.25, 15.85, 18.25, 19.85, 23.05 or 23.85 kbit/s. The sound quality after AMR-WB compression is generally much better than with the AMR-NB compression. Audio files with audio streams encoded using the AMR-WB compression usually have the extension .awb
- AMR-WB+ (Extended Adaptive Multi-Rate – Wideband) – the latest variant of AMR compression provides high sound quality, which uses sampling frequency of 16, 24, 32 or 48 kHz, and a bitrates from 5.2 to 48 kbit/s.
AMR files can be played using some software players (eg VLC, MPlayer). Unfortunately, most portable players (except mobile phones) and almost all fixed players do not support AMR format.
AMR to MP3 conversion using Pazera Free Audio Extractor
Starting the program and adding AMR files to the processing list
When you install and run the program, the main window will appear.
To convert AMR files, you must first add them to the processing list. To do this, click the button and specify the desired AMR files. They appear on the list. Files can also be added using drag and drop.
Parameters of the AMR to MP3 conversion
When you add files to the list, the next step is to set the output format to MP3 – MPEG-1 Layer 3 in the Audio section.
Then select the audio bitrate that will be used while conversion. You must remember that AMR files are usually encoded with a very low bitrates (AMR-NB up to 12.2 kbit/s, AMR-WB up to 23.85 kbit/s and AMR-WB+ up to 48 kbit/s), so the bitrate of AMR to MP3 compression is best to set to a relatively low value. On the other hand, the MP3 encoder not very good handles the audio compression at very low bitrates, so it is recommended to set a little bit higher bitrate than the value of this parameter in the source file. At least 24 or even 32 kbit/s.
If you set audio bitrate in the Auto position, the minimum value of the bitrate used during encoding to MP3 will be 32 kbit/s. If the source file has been encoded with a bitrate higher than 32 kbit/s, the program will automatically set the bitrate of audio encoding to the same value (or similar) as in the source file.
When you set the Sampling frequency and Channels to Auto, then the values of both parameters in the generated MP3 file will be the same as in the source AMR file (for AMR-NB: 8kHz and one audio channel).
Using the Volume slider you can adjust the sound level in the resulting MP3 file. When set to 1x, the volume will not change.
At settings suggested above, during conversion of AMR files to MP3 will be used very low values of bitrate and sampling frequency. If your player can not play MP3 file created with that settings, check in the documentation the minimum bitrate and sample rate of MP3 files supported by this player.
If you do not have access to the documentation, try the conversion settings shown in the picture below:
Starting conversion
When you add AMR files to the processing list and set all the necessary parameters, you can already start the conversion by clicking the button. The Conversion window will appear, where you can track the progress of the operation.
With default settings, the converted files will appear in the same directory that contains the source files. You can change output folder in the Output section. Generated MP3 files will have the same name as AMR files, only the extension is changed to .mp3.