VOCAL’s iOS VoIP Libraries are optimized for application developers to meet unique Voice over IP (VoIP) application requirements for mobile devices, including speech coders, acoustic echo cancellation (AEC) and noise cancellation. These libraries are developed in C/C++ for use with the iOS SDK. Developers can access VOCAL’s iOS VoIP application software using Objective C. VOCAL’s embedded software supports a complete range of ETSI / ITU / IEEE compliant algorithms. Our modular Libraries enable rapid development of mobile apps using field-tested standards-based software.
The VoIP stack provides access to the Vocoder Library and incorporates an adaptive jitter algorithm to further enhance voice quality. The proprietary jitter algorithm is exceptional at adapting to packet loss or delays from congested networks while maintaining constant audio output for the listener.
A native network stack and VoIP protocols implement an iOS SIP client which provides full access to VoIP Internet calling and other services using SIP and RTP. Video conferencing and streaming are also supported with RTP. In addition, VoIP encryption using SRTP or TCP with TLS is available for secure SIP client communications.
The VOCAL Modular VoIP Stack includes a selection of iOS vocoders for developers to customize applications for unique voice codec requirements. VOCAL’s native libraries include the standard audio codecs G.711, G.722, G.722.1, G722.2, G.729, G.729A, G.729AB, as well as the low bit rate MELPe vocoder and the OPUS interactive audio codec. Additional voice codecs are available from VOCAL upon request. The following iOS vocoders are currently available for use in mobile VoIP calling and SIP client applications.
- G.711 - 64k bps PCM (A-law or μ-law form)
- G.722 - 7 kHz audio coding within 64 kbit/s (SB-ADPCM)
- G.722.1 - 24k and 32k bps, 7 kHz audio
- G.722.2 - Adaptive Multi-Rate Wideband (GSM AMR-WB)
- G.729AB - 8k bps CS-ACELP
- MELPe – Mixed-Excitation Linear Predictive Enhanced
- OPUS - 8kHz to 48kHz audio with dual layer LP and MDCT encoding
The iOS Vocoder Library provides acoustic echo cancellation, dereverberation, and noise reduction algorithms. AEC removes reflected copies of a direct path wave from the acoustic/mechanical coupling between speaker and microphone; dereverberation addresses reflections from surfaces in an enclosed environment; while noise reduction reduces additive noise sources. Together the techniques provide enhanced speech in iOS applications.
Acoustic beamforming algorithms are provided in the libraries to capture the speaker’s voice. Mobile devices are increasingly used as speakerphone systems where the microphone is removed some distance from the speaker. Beamforming can be used with microphone arrays to focus in the direction of the speaker and minimize background noise from other directions.
- Optimized performance for iOS devices
- VoIP stack supports SIP client applications
- Multi-tasking and multichannel operations
- Full and half duplex modes
- Compliant with ITU standards
- Voice and video over Wireless LAN
- Wideband IP telephony
- Audio and video conferencing
- Fax over IP