HD-Voice for cellular communications - Khariton, Dmitry, Vladimir, Oleg, Irina, Glory!



    We turned on HD-Voice on the Beeline network in Moscow. Below are sound recordings before and after, as well as technical details.

    The HD-voice mode is based on the AMR-WB technology (Adaptive Multi Rate Wadeband) - adaptive broadband coding with variable speed, this codec is also known as the G.722.22 standard. In theory, a person can hear sounds in the range of 20Hz - 20kHz, but in practice it is enough to transmit sound in a much narrower range. When encoding speech in AMR-WB, the frequency range of 50Hz-7kHz is used, this is absolutely enough for full voice transmission. For example, the AMR codec uses the 300-3 kHz range. The method can be used on 2G and 3G networks.

    Simply put, now the human voice will sound more natural, because it will cease to “squeeze” into a rather narrow strip, the need for which was once dictated by the limitations of infrastructure. In addition, with HD coding, external noise has less impact on speech intelligibility.

    How did we get to HD-Voice, and how does it work?


    A person is able to hear a certain band of sound frequencies, usually it is taken equal to 20Hz-20kHz. It is difficult to transmit the entire spectrum via wireless communication channels without compression, so voice without band cuts is transmitted only in wired systems. For the purpose of speech compression, voice codecs or vocoders are used. Their side effect is the distortion of the transmitted voice by limiting the frequency band of the voice message.

    The very first voice codec used on mobile networks was “Full Rate” - FR. Simultaneously with FR, the Half Rate codec was also introduced, its sole purpose is to increase the number of simultaneously served subscribers, and, as its name implies, it occupies half the band of the FR codec in the radio channel. However, the voice quality after transcoding to FR was not very high, and for some countries (for example, Arab, where the speech speed is high and there are a lot of high-frequency sounds), is completely unacceptable. Therefore, the FR codec was redesigned and the Enhanced Full Rate appeared, providing significantly better voice quality with less bitrate being created.

    With the growth of mobile network penetration, requirements for the quality of voice services began to grow, and there was a problem with the deterioration of voice quality, with a low level of radio signal from the base station. To solve this problem, a new codec was developed - “Adaptive Multi Rate”, which used the same frequency range for analysis and compression, but the algorithm was implemented in such a way that the bitrate of the codec changed dynamically, depending on the quality of the received signal. Thanks to this, it was possible, with good radio conditions, to provide excellent voice quality, and with bad conditions, to keep a conversation even where FR / EFR codecs could not work at all.

    All 3G networks work only using the AMR codec or its subsequent implementations, for example AMR-WB. But since there are still a large number of subscribers using phones that only support EFR / HR codecs, the 2G network continues to work with all codecs (FR / EFR / HR / AMR FR / AMR HR) immediately, providing voice communications to any phone.

    Currently, voice quality requirements in mobile networks continue to grow, and it is time to use AMR-WB technology. All codecs described above use a frequency range up to 200Hz-3.4kHz for compression, while AMR-WB uses a voice message bandwidth of 50Hz-7kHz for encoding., I.e. AMR-WB allows you to transmit twice the large frequency band, which gives an increase in the quality and saturation of high and low frequencies of the transmitted voice.

    Some codec specifications are listed in the table:

    Codec

    Standard

    Year of creation

    Range of compressible frequencies

    Created Bitrate

    Full Rate - FR

    GSM 06.10

    1990

    200-3400 Hz

    13 kbit / s

    Half Rate - HR

    GSM 06.20

    1990

    200-3400 Hz

    5.6 kbit / s

    Enhanced Full Rate - EFR

    GSM 06.60

    1995

    200-3400 Hz

    12.2 kbit / s

    Adaptive Multi Rate - AMR

    3GPP TS 26.071

    1999

    200-3400 Hz

    4.75 - 12.20 kbit / s

    Adaptive Multi Rate - WideBand - AMR-WB

    3GPP TS 26.190

    2001

    50-7000 Hz

    6.60 - 23.85 kbit / s

    Adaptive Multi Rate-WideBand + - AMR-WB +

    3GPP TS 26.290

    2004

    50-7000 Hz

    6 - 36 kbit / s (mono)
    7 - 48 kbit / s (stereo)



    Hint for curious programmers: a sample implementation of the AMR codec in C is available in the 3GPP TS 26.073 standard (you can easily find, download and try to implement it).

    In the diagram below, you can see a comparison of voice quality, according to the MOS (Mean Opinion Score) scale, depending on the codec used. The MOS scale is a subjective assessment of voice quality from 0 to 5, where 0 is the complete absence of audibility, and 5 is live speech. G.711 codec - used in landline telephony, that is, this is the quality that you should hear from your landline phone (unless, of course, it has been transferred to the IP channel, but this is a topic for a completely different conversation).



    Update: The comments rightly pointed out that the average MOS score for the G.711 codec is about 4.1, this picture slightly distorts reality.
    As you can see from the diagram (and taking into account the information from Update), the AMR-WB codec provides, with good radio conditions, voice quality similar to that which we are used to when using a wired home telephone.

    For example, two fragments of a musical composition, which were compressed by AMR and AMR-WB codecs, you can compare the sound quality yourself and visually evaluate the difference in the sound picture created by different codecs.

    AMR encoded upper track

    AMR-encoded lower track

    Tests


    We are not the first to launch this technology in Russia, so there have already been some developments. Our first network segment with HD-Voice was built within the Moscow Ring Road, using Ericsson equipment. Activating AMR-WB took a long time: at first it was tested on one controller (with numerous drive tests for measuring speech quality). And even after everything was tested on one controller, the subsequent activation took place in stages, controller after controller. The entire activation process took almost six months.

    Here are the reference samples from the final tests , which were evaluated in hardware using accurate measurements at different times.

    Does it already work?


    Yes, now the technology is implemented in a 3G network for Moscow. In order to use the mode, you do not need to make additional settings, it activates itself if both subscribers are on the 3G network and both of their phones support the codec.



    The diagram shows the conditions that are necessary for the operation of the AMR-WB. Now, as mentioned above, the codec is launched on a 3G network, the next step is to ensure the codec works between a 2G and 3G network, then between networks and between operators.

    What devices are supported?


    List. Caution, there are a lot of letters under the spoiler.
    Alcatel One Touch 903
    Alcatel One Touch 916 / 916D
    Alcatel One Touch 918
    Alcatel One Touch 983
    Alcatel One Touch 985 / 985D
    Alcatel One Touch 991 / 991D / 991T
    Alcatel One Touch 992D
    Alcatel One Touch 993 / 993D
    Alcatel One Touch 995/996
    Alcatel One Touch Idol
    Alcatel One Touch Idol Ultra
    Alcatel One Touch Scribe Easy
    Alcatel One Touch Scribe HD
    Alcatel One Touch Star
    Alcatel One Touch Tribe
    Alcatel One X'POP
    Apple iPhone 5
    Apple iPhone 5S
    Apple iPhone 5C
    BlackBerry Q10
    BlackBerry Q5
    BlackBerry Torch 9810
    BlackBerry Z10
    BlackBerry Z30
    HTC Desire 500
    HTC ChaCha
    HTC Desire C
    HTC Desire HD
    HTC Desire S
    HTC Desire X
    HTC Desire Z
    HTC EVO 3D
    HTC Incredible
    HTC One
    HTC One mini
    HTC One S
    HTC One SV
    HTC One V
    HTC One X
    HTC One X +
    HTC One XL
    HTC One (M8)
    HTC Radar
    HTC Raider
    HTC Rhyme
    HTC Sensation
    HTC Sensation XE
    HTC Sensation XL
    HTC Titan
    HTC Touch HD
    HTC Wildfire S
    HTC Windows Phone 8X
    HTC Windows Phone 8S
    Huawei Ascend D Quad
    Huawei Ascend D2 LTE (VoLTE)
    Huawei Ascend G510
    Huawei Ascend G740
    Huawei Ascend P1 U9200
    Huawei Ascend P2
    Huawei Ascend P6
    Huawei Boulder U8350
    LG A310
    LG Nexus 4 E960
    LG Nexus 5
    LG Optimus 3D
    LG Optimus G
    LG Optimus G Pro
    LG Optimus L4 II
    LG Optimus L5
    LG Optimus L5 II
    LG Optimus L7
    LG Optimus L7 II
    LG Optimus L9
    LG Optimus LTE2 F160LV (VoLTE)
    LG Optimus F7
    LG Optimus F180S (VoLTE)
    LG Optimus Vu2 F200 (K, L, S) (VoLTE)
    LG Optimus Vu3 F300 (K, L, S) (VoLTE)
    LG Optimus GX F310L (VoLTE)
    LG Optimus G2 F320S (VoLTE)
    LG Optimus G Pro F240S (VoLTE)
    LG Optimus LTE III F260S (VoLTE)
    LG Optimus G Flex F340S (VoLTE)
    LG Optimus 3D Max (P720)
    LG Optimus 3D (P920)
    LG Optimus 4X HD (P880)
    LG Prada (P940)
    LG Prada 3.0
    Motorola Quench
    Motorola RAZR (XT910 )
    Motorola RAZR i (XT890)
    Motorola Moto G
    Nokia 300
    Nokia 301
    Nokia 302
    Nokia 500
    Nokia 515
    Nokia 600
    Nokia 603
    Nokia 700
    Nokia 701
    Nokia 808 PureView
    Nokia 5230
    Nokia 5330 Mobile TV Edition
    Nokia 5530 XpressMusic
    Nokia 5630 XpressMusic
    Nokia 5730 XpressMusic
    Nokia 6260 Slide
    Nokia 6600i slide
    Nokia 6700 classic
    Nokia 6700 slide
    Nokia 6710 Navigator
    Nokia 6720 classic
    Nokia 6760 slide
    Nokia 6790 slide
    Nokia 7230
    Nokia Asha 300
    Nokia Asha 301
    Nokia Asha 302
    Nokia Asha 303
    Nokia Asha 311
    Nokia C2-01
    Nokia C3-01 Touch and Type
    Nokia C5-03
    Nokia C5-04
    Nokia C6-00
    Nokia C6-01
    Nokia C7-00
    Nokia E5-00
    Nokia E52
    Nokia E55
    Nokia E6-00
    Nokia E63
    Nokia E7 Communicator
    Nokia E7-00
    Nokia E71x
    Nokia E72
    Nokia E73 Mode
    Nokia Lumia 510
    Nokia Lumia 520
    Nokia Lumia 520.2
    Nokia Lumia 521
    Nokia Lumia 610
    Nokia Lumia 610 NFC
    Nokia Lumia 620
    Nokia Lumia 625
    Nokia Lumia 710
    Nokia Lumia 720
    Nokia Lumia 800
    Nokia Lumia 810
    Nokia Lumia 820
    Nokia Lumia 822
    Nokia Lumia 900
    Nokia Lumia 920
    Nokia Lumia 920T
    Nokia Lumia 925
    Nokia Lumia 925 Superman Edition
    Nokia Lumia 925T
    Nokia Lumia 928
    Nokia Lumia 929 LTE-A (Cat 4)
    Nokia Lumia 1020.2
    Nokia Lumia 1020 3G
    Nokia Lumia 1020 LTE
    Nokia Lumia 1520
    Nokia N7
    Nokia N8
    Nokia N86 8MP
    Nokia N9
    Nokia N97
    Nokia N97 mini
    Nokia X3-02
    Nokia X5
    Nokia X6-00
    Nokia X7-00
    Samsung Galaxy Star
    Samsung Galaxy Light
    Samsung Ativ S
    Samsung Galaxy Ace
    Samsung Galaxy Ace 2
    Samsung Galaxy Express
    Samsung Galaxy Fame
    Samsung Galaxy Mini
    Samsung Galaxy Mini 2
    Samsung Galaxy Nexus
    Samsung Galaxy Note
    Samsung Galaxy Note II
    Samsung Galaxy Note 3
    Samsung Galaxy Note 10.1
    Samsung Galaxy S II
    Samsung Galaxy S III
    Samsung Galaxy S4
    Samsung Galaxy S4 Mini
    Samsung Galaxy S5
    Samsung Galaxy S Advance
    Samsung Galaxy S Plus
    Samsung Galaxy W
    Samsung Galaxy Y
    Samsung Omnia 7
    Samsung Omnia Pro B7350
    Samsung S5610
    Samsung Wave 3
    Samsung Trend Plus
    Sony Ericsson Elm
    Sony Ericsson Hazel
    Sony Ericsson Live with Walkman
    Sony Ericsson Xperia X8
    Sony Ericsson Xperia X10 Mini
    Sony Ericsson Xperia X10 mini pro
    Sony Ericsson Xperia acro
    Sony Ericsson Xperia active
    Sony Ericsson Xperia Arc
    Sony Ericsson Xperia arc S
    Sony Ericsson Xperia mini
    Sony Ericsson Xperia Mini Pro
    Sony Ericsson Xperia neo
    Sony Ericsson Xperia neo V
    Sony Ericsson Xperia Play
    Sony Ericsson Xperia ray
    Sony Ericsson W995
    Sony Xperia A SO-04E
    Sony Xperia acro S
    Sony Xperia E
    Sony Xperia E dual C1605
    Sony Xperia Go (ST27i)
    Sony Xperia i1 HSPA + C6902
    Sony Xperia i1 LTE
    Sony Xperia ion
    Sony Xperia J
    Sony Xperia L
    Sony Xperia M
    Sony Xperia M35t (VoLTE)
    Sony Xperia miro
    Sony Xperia P
    Sony Xperia S
    Sony Xperia Sola
    Sony Xperia SP
    Sony Xperia T
    Sony Xperia Tipo
    Sony Xperia Tipo Dual
    Sony Xperia U
    Sony Xperia V
    Sony Xperia Z
    Sony Xperia ZL
    Sony Xperia ZR
    Sony Xperia Z1
    Sony Xperia Z1S (T Mobile US only)
    Sony Xperia Z1 Compact LTE-A D5503
    Sony Xperia Z2 LTE-A D6543 / D6503
    TechFaith Wildfire 80
    ZTE Blade V880
    ZTE Crescent (San Francisco 2 on Orange)
    ZTE Era
    ZTE F160 Atlanta
    ZTE Grand X
    ZTE Grand X IN
    ZTE Orbit
    ZTE R252 / Orange Tara
    ZTE Kis Pro / Orange Zali
    ZTE Skate (Monte Carlo on Orange)
    ZTE Smart Netphone 701
    ZTE Tania
    ZTE TMN smart A15


    Recognition problems


    Human speech is such that the sounds “C” and “F” are poorly distinguished in the radio and on a narrow band of the audio spectrum. The pairs “T” and “P”, “M” and “H” also suffer. Hence the mnemonic system with the names: "I dictate, Olga’s number two, zero, zero, three, as I understand it, the reception?" Things grow out of here, like assigning the most critical parts of the callsigns with “p” - for example, a sniper, who in no case should confuse his callsign, most likely will be “thirty-third”, because on the air this is very distinguishable in narrow stripes.

    Also with HD-Voice voice recognition is growing. This is important for personal communication, and for the growing popularity of additional authentication by voice, for example, in banks.

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