LTE Voice Codec AAC-ELD

We are using mp3 file format generally in our computers and mobile phones to be able to listen music.  In reality, we are not listening original sound there.  Original sound is sort of raw data and we are just hearing compressed version of original sound.

 Raw Voice
Raw voice for example 16 bit 44 kHz wave format (.wav) 3 minutes will be approximately 30 megabytes. This is very huge size. If it is compressed into 128Kbps mp3 then it is around 3 megabytes. Simply, we can see that file size significantly decreases if we use codec.

 

 

What is Codec?

Codec is a short name for coder-decoder the software that takes a raw data file and turns it into a compressed file. An audio codec is a device or computer program capable of coding or decoding a digital data stream of audio.  Because of original sound size is big, we need to use codec for many perspectives like network stability etc.

GSM Codecs.

In GSM history, many codec types  have been developed.  These are;

Half Rate (HF)

Full Rate (FR)

Enhanced Full Rate (EFR)

 EFR introduced in 1997

Adaptive Multi Rate – Narrow Band (AMR or AMR-NB)

This is using in GSM and UMTS, introduced in end of 1990s.

Adaptive Multi Rate – Wide Band (AMR-WB)

Improved version of AMR due to a wider speech bandwidth compared to AMR Narrowband. It is commercially released in 2008. Also this is introduction with HD-Voice quality.

Advanced Audio Coding – Enhanced Low Delay

This is final developed codec for GSM World and using in LTE networks. This codec is designed for  Full-HD Voice. To be able to reach full HD voice quality,  codec  has to support  ~20khz frequency.  To compare differency; previously explained  HD-Voice branded codec  AMR-WB   supports only 7kHz.By the way, very important point is, both network and handsets have to support this feature.
 

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