16th December 2011
Twenty years ago I worked in an office where one desk phone was shared between four engineers and email was sent and received by the server twice a day. Today on my desk are four phones (two desk VoiP phones, mobile phone, PC headset) and email between desktop, phone and the rest of the world that takes seconds.
Each of the four phones sounds different. The worst call quality is international mobile-to-mobile and the best is PC to PC. The desk phones are made by different companies and fall somewhere in between. I’ve noticed that I strain to understand the conversation far less on the PC calls, so the calls feel more relaxed. So I wondered how much of the variability is due to the mics and speakers, how much to the analogue circuitry and how much to the software CODECs (which compress the speech to transfer it using less capacity).
The voice can certainly go through a lot of processing. The mic connects to an ADC, to convert the analogue mic signal to a digital signal. It then gets compressed by an audio software CODEC. These CODECs work in different ways, depending on whether it’s a DECT cordless handset, Bluetooth headset, GSM phone or 3G/CDMA phone. And in many cases a different one will be converting the compressed data back to voice; then there is the DAC, speaker ampflifier and speaker. The most efficient CODECs don’t even transmit your voice, but instead have an artificial throat model and send instructions on how to stimulate it so it sounds similar to your voice. This poses many challenges to a world which has different ways of speaking.
With all this processing, it’s amazing how good call quality can be around the globe. Despite all the software CODECs, here at Wolfson we focus on the world of digital to analogue to acoustic conversion. The mechanical parts are the most variable in their performance and intimately connected with their surrounding acoustic environment. We see this environment has a huge part to play in the intelligibility of voice and have developed expertise in this. We are actively working on making significant improvements in this area with signal-processing enhancements and I look forward to owning a mobile phone with these improvements to make my calls more relaxed.
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