The higher the compression the less is the number of bits per second during a voice call. It is up to the user of the GSM / UMTS module to select the compression. If the battery capacity is the issue, then the half rate is maybe a good choice. If the audio quality is more important, then standby time the Enhanced Full Rate is a good choice. If you use the microphone of GSM / UMTS module to listen in and to record the voice dialogue of the thefts detected by burglar alarm system, then a good audio quality will help the police to analyse the recording. If you do the same with a people tracker for Alzheimer patients, then Half Rate is the better choice, because saving the battery is maybe more important. For communication systems at door entry or in an elevator it makes sense to select highest audio, because power consumption is often less important.
This voice codec was first standard used in GSM. Its average bit rate is 13 kbit/s. The quality of speech is less by modern standards, but was a good compromise between complexity and quality. The codec is still usually used in networks around the world. Step by step FR will be replaced by Enhanced Full Rate and Adaptive Multi-Rate, which offer much higher speech quality with a lower bit rate.
It is operating at 5.6 kbit/s and needs the half bandwidth of the Full Rate codec, network capacity for voice traffic is doubled, at the expense of audio quality. It is suggested to use it when the battery
is low because it saves 30 % more energy. The sampling rate is 8 kHz with resolution 13 bit.
Enhanced Full Rate / EFR / GSM-EFR / GSM 06.60
It is working at 12.2 kbit/s. The EFR provides wire-like quality in any noise free and background noise conditions. The EFR 12.2 kbit/s codec is compatible with the highest AMR mode (AMR_12.2). Enhanced Full Rate helps to improve the call quality. The codec consumes about 5 % more energy. It uses link adaptation to select from one of eight different bit rates based on link conditions.
It is also a file format for storing spoken audio. Many modern mobile phones will allow you to store short recordings in the AMR format. Open source and commercial programs exist to convert between this and other formats such as MP3. It should be remembered that AMR is a speech format and is unlikely to give ideal results for other audio (e.g music). The common filename extension is .amr. There also exists another storage format for AMR that is suitable for applications with more advanced demands on the storage format, like random access or synchronisation with video. This format is the 3GPP-specified 3GP container format based on ISO base media file format.