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Home > HPC > EVS Voice Codec
3GPP reference code encoded and decoded output displayed side-by-side with HPC EVS Voice Codec output
The HPC EVS voice codec is intended for high capacity, high reliability VoLTE (Voice-over-LTE) telecom systems

EVS Codec (EVS Voice Codec)


The EVS Codec (Enhanced Voice Services Codec) is a new generation of HD voice codec standardized by 3GPP for VoIP and VoLTE applications (*). The HPC EVS codec is Signalogic's optimized and robust implementation, fully compliant with 3GPP standards and intended for use in high capacity, high reliability telecom and enterprise systems.

The HPC EVS codec is currently being deployed in major carriers and networks; here are key reasons why:

The HPC EVS codec is a library module in SigSRF software, which includes packet, streaming, voice, algorithm, diagnostic, inference, and other library modules. SigSRF combined with EVS and other codecs offers solution functionality including:

Demo versions run on Linux servers with mediaMin and mediaTest reference applications for telecom, analytics, lawful intercept, and more. Customized, application-specific trial / eval versions are also available. Online demos include codecs for AMR-NB, AMR-WB, and G711. Customized trial / eval versions can include additional codecs.

(*) 3GPP Overview

Product Info

HPC EVS Voice Codec Encoder Lib Software     HPC EVS Voice Codec Decoder Lib Software     HPC EVS Voice Codec Common Lib Software

CIM32 PCIe Card

CIM64 PCIe Card

Signalogic Logo
Description HPC EVS Voice Codec
Product Categories HPC (High Performance Computing), Media Resource Functions, Algorithms
Product Status New Introduction

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Product Description -- EVS Features

Sampling Rates (kHz)

8, 16, 32, 48

Mode / Bandwidth (Hz)

NB (Narrowband) / 20 - 4000

WB (Wideband) / 20 - 8000

SWB (Super Wideband) / 20 - 16000

FB (Fullband) / 20 - 20000

Bitrates (kbps)


     7.2, 8, 9.6, 13.2, 16.4, 24.4


     7.2, 8, 9.6, 13.2, 16.4, 24.4, 32, 48, 64, 96, 128


     9.6, 13.2, 16.4, 24.4, 32, 48, 64, 96, 128


     6.4, 24.4, 32, 48, 64, 96, 128

NB & WB VBR (Variable bitrate)

     Average of 5.9

Jitter Buffer

Both internal JBM and SigMRF voice framework JBM are supported


Fully re-entrant and multichannel, XDAIS compliant


Supported. DTX (VAD) can be applied at SDP level on per
session basis, or automated if VBR mode is enabled


Advanced PLC (Packet Loss Concealment) techniques supported.
See "RF Channel Aware Mode" description below

Framework Options

Can be used with SigMRF voice framework software to enable
DTMF, echo cancellation, sampling rate conversion, variable ptime,
tone generation, and other audio and RTP processing

2G/3G Compatibility

AMR-WB Compatibility Mode


Bit-exact libraries are available with approx 30% reduction in
performance. For standard high performance libraries, audio
quality is indistinguishable from bit-exact version and can be so
demonstrated by signal analysis software

3GPP EVS code version



RF Channel Aware Mode

To support high definition voice in LTE enabled networks, the EVS codec provides a "channel aware" mode of operation that applies state-of-the-art packet loss concealment (PLC) techniques against channel induced bit errors, both single bit and burst. In the case of telecom and enterprise applications, the mode is also referred to as "RF channel aware" as in this case bit errors may occur in transmissions between cell towers, basestations, and handsets, WiFi connections, and other RF links in the transmission chain.

Paraphrasing from "Improved error resilience for VoLTE and VoIP with 3GPP EVS channel aware coding" (*):

The newly standardized 3GPP EVS speech codec contains a highly error resilient mode called "channel aware". Compared to prior generation codecs, EVS' channel aware mode offers significantly improved error resilience in voice communication over packet-switched networks such as Voice-over-IP (VoIP) and Voice-over-LTE (VoLTE). Error resilience is achieved using a form of in-band forward error correction (FEC) and source-controlled coding techniques to identify candidate speech frames for bitrate reduction.

The process described in the article leaves available bits for transmission of partial copies of prior frames, while still maintaining the required bitrate. Even in the case of lost or discarded primary frames -- which tends to be the end result of bit errors in packet switched networks -- voice quality stays within an acceptable range. The article gives MOS test results to demonstrate this voice quality robustness.

(*) Authors V. Atti, D.J. Sinder, S. Subasingha, and V. Rajendran, as published in "Acoustics, Speech and Signal Processing (ICASSP), 2015 IEEE International Conference on" on 24Apr15


Capacity Figures

The following table gives per core capacity figures for x86 (2.2 GHz, Xeon E5-2660 v0, 32 nm) and c66x (1.6 GHz, C6678 v2.0, 45 nm). All figures are physical core, not hyperthreaded or virtual core. For any figures in the table not yet uploaded, please inquire.

Per Core EVS Codec
Capacity Figures 1

Bitrate (kbps)





Sampling Rate (kHz)













































1 Figures given for concurrent encode and decode (transcode) between G711 and EVS, DTX disabled.


The following table gives capacity figures for some example x86 and c66x platforms.

Platform EVS Codec Capacity Figures 2

Number of CPUs

Clock Rate (GHz)



1U server with sixteen (16) x86 cores 3

2 2.2 480

1U server with 128 c66x cores 4

16 1.6 3712

ATCA board 5

20 1.25 3625

2 Figures given for concurrent encode and decode (transcode) between G711 and EVS at 16 kHz (WB), 13.2 kbps, DTX disabled
3 Xeon E5-2660 at 2.2 GHz
4 C6678 at 1.6 GHz
5 C6678 at 1.25 GHz

Applications and API Interface

The HPC EVS codec is suitable for the following applications:

API calls available to applications include:

API header files are availble for inspection, upon request.

As a CPU and C/C++ based product, the HPC EVS voice codec is easy to modify. Application specific features can be added if needed under NRE contract.

Test and Measurement

mediaMin and mediaTest are reference user applications based on SigSRF (Streaming Resource Function) modules. mediaMin and mediaTest include:

mediaTest is an indispensable diagnostic tool, increasing test and measurement efficiency twentyfold vs. the old JTAG emulator method. By accepting and generating .wav and .cod formats, mediaTest data files are directly interchangeable with 3GPP reference code. To facilitate UDP/RTP mode testing, utilities are included to extract pcap data and create valid .cod files, including ToC header byte, in both header-full and compact-header formats.

Below is a packet data flow diagram showing coCPU packet data flow and network I/O options available to user applications and the mediaTest demo application:

coCPU™ packet data flow and network I/O options
coCPU™ packet data flow and network I/O options using the mediaTest demo app or user applications

mediaTest Demo

The SigSRF SDK download page contains free, limited demo version of the mediaTest software for test and measurement purposes, along with several mediaTest command line examples.

Why Signalogic ?

Modern HPC methods have changed the nature of optimization. Unlike legacy codec providers, Signalogic approaches high capacity telecom and enterprise applications from an HPC perspective, not only for implementation but for testbed and audio quality control. We use banks of heterogeneous CPU servers to automate portions of the optimization process for HPC libraries, including highly complex applications such as real-time image analytics (for example, see our c66x OpenCV page). This is called "automated programming" and is one of the exciting new areas of AI you will hear about over the next few years. In the case of speech transcoding such as EVS, the objectives are relatively simple compared to other applications, so we can apply our new techniques in their early stages -- and the capacity results speak for themselves.

In addition to EVS, Signalogic has an established position in telecom and related enterprise applications with a variety of software components currently deployed, including SigMRF voice framework, high performance network stacks, and other codecs. Combined with our NFV transcoding solution, we understand how transcoding, data plane / DPDK, and fast path pieces fit together, how to achieve 99.999% reliability, and how to provide effective technical support in the demanding Tier 1 carrier environment.

For more information on Signalogic's HPC solutions for servers with combined TI and Intel CPUs, see the HPC overview and NFV Transcoding pages on TI's website.

Software Only vs. coCPU™

"Software only" is a marketing term meaning "x86 hardware". Typically the term is used to exclude specialized, non-CPU devices such as GPUs, ASICs, DSPs, FPGAs, etc, and emphasize ease-of-use and widespread software support. A more accurate term is coCPU™, which allows for host and coCPUs while at the same time continuing to emphasize ease-of-use and software support benefits. In a coCPU™ system, all CPUs are (i) peers, allocated and utilized as needed by the OS, VMs, OpenStack, etc, and (ii) coherent, able to coordinate high-speed data and results.

The HPC EVS Codec is a coCPU™ solution. This means it can run on x86 only, c66x only, or a combination of both CPU types. Conversely, this also means the solution does not run on GPUs, ASCIs, and FPGAs. The following characteristics are required for a coCPU solution:

The HPC EVS codec meets these requirements: (i) it consists of three libraries (encoder, decoder, and common), (ii) it's optimized using a variety of techniques applicable to C/C++ coding (which also makes it easy to modify / enhance as 3GPP standards continue to evolve, and to add application specific features as may be needed), and (iii) it's compatible with the DirectCore coCPU software stack.

Below is a list of platform and CPU combinations supported:

Platform and CPU


None 1


Other c66x 2



Server 3

Server 3, 4










1 x86 only
2 Includes C6670, C6657, TCI6608, TCI6614, TCI6614, TCI6618
3 Supported by mediaTest
4 Includes rackmount 1U, 2U, etc. and small form-factors such as mini-ITX

3GPP Reference Codes

3GPP reference C codes are available online in fixed-point and floating-point code bases.

The 3GPP codes are not intended for commercial use, instead serving two fundamental purposes (i) generic C code that can be ported and optimized for specific CPUs and platforms, and (ii) "bit exact" comparison to ensure correct results after any changes are made. The following requirements must be addressed for commercial operation:

To address the first two requirements, the HPC EVS codec implements thread-safe encoder and decoder instances. This allows the HPC EVS codec API interface to support several modes of operation, including frame data, packet data, and complete packet flow (see the Applications and API Interface section above for detailed information). To address the third requirement, the HPC EVS codec implements numerous optimizations, and also supports server capacity expansion with coCPU cards, in increments of 64 coCPU cores per card.

As noted above under "Test and Measurement", data file formats used by the 3GPP reference code are compatible with the mediaTest app.

Related Applications

The HPC EVS voice codec can be used with the following related applications:

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Related Items

1) Codec Wav Samples, before and after encode/decode

2) mediaMin and mediaTest demo
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mediaTest high capacity media session transcoding screen capture, showing EVS performance benchmarking in diagnostic mode

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Tech Support

Signalogic's engineering staff designs, develops, maintains, operates, and tests software and hardware in the company's in-house lab, using servers from HP, Dell, Supermicro, Artesyn, Advantech, and others, and Linux installations including CentOS, Ubuntu, Red Hat, Wind River, Gentoo, and more. Customers can submit technical questions via e-mail, phone, or Skype chat.

Signalogic engineers are experts in server and embedded system development. Unlike retailers and distributors Signalogic can also perform contract development. Signalogic is a member of third-party programs for HP, Dell, Intel, and Texas Instruments. A high level of expert tech support is a distinct advantage when purchasing products from Signalogic.