How Does Voice Compression in VoIP Work

Teenagers talking via video call

Alex Segre / Getty Images

There are so many factors affecting voice quality: the broadband connection, bandwidth, hardware, software and the technology itself. The bandwidth, hardware, and software factors are in our control — we can change and tweak and improve on them; so when we speak of voice quality in VoIP, we often point a finger to the underlying technology itself, something which is beyond our control as users. A prominent element of VoIP technology is data compression.

What Is Data Compression?

Data compression is a process whereby voice data is compressed to render it less bulky for transfer. Compression software (called a codec) encodes the voice signals into digital data that it compresses into lighter packets that are then transported over the Internet. At the destination, these packets are decompressed and given their original size (though not always), and converted back to analog voice again, so that the user can hear.

Codecs are not only used for compression, but also for encoding, which, simply said is the translation of analog voice into digital data that can be transmitted over IP networks.

The quality and efficiency of the compression software, therefore, has a big impact on the voice quality of VoIP conversations. There are good compression technologies and there are less good ones. Better said, each compression technology is designed for a specific use under specific circumstances. After compression, some compression technologies incur some loss in terms of data bits and even packets. This results in bad voice quality.

VOIP and Voice Compression

VoIP encodes and compresses voice data in a way such that some of the elements of the audio stream is lost. This is called lossy compression. The loss is not a hard blow on voice quality as much of it is on purpose. For instance, sounds that cannot be heard by the human ear (of a frequency below or beyond that of the hearing spectrum) is discarded since it will be useless. Also, silence is discarded. Minute fractions of audible sound is lost as well, but tiny bits lost in voice does not prevent you from understanding what is being said.

Now, if your service provider uses the right compression software, you will be happy; else you might have to complain a little bit. Today, compression technologies are so advanced that the voice output is nearly perfect. But a problem lies with the choice of the compression software: different compression software adapts to different needs. For instance, there are some for voice, some for data and some for fax. If you try sending a fax using voice compression software, the quality will suffer.

Data compression, when efficiently developed and used, can be the very element that thrusts VoIP above landline phone in terms of voice quality, and make it better. This can be possible as long as the other factors (bandwidth, hardware, etc.) are favorable. Since compression lightens ​the load of data to be transmitted in a certain amount of time, better results can be achieved.