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IPfocusBack to basics AudioTechnology explained for mortals:Inevitable delay when distributing Audio over IPWhenever you transport audio over an IP network -this is true for every vendor and every technology,you will incur a delay. This is unavoidable. Why ?Audio needs to be sampled into the digital domainat the encoder, and packetized to keep the networkload in check. Depending on the application, codecused and the requirements, the amount of samplescollected before sending will be between 1ms androughly 100ms. This is the delay introduced by anoptimized encoder, assuming no further processingor buffering, with PCM or low computationalcompression algorithms.With MP3, an additional delay will be introduced,due to the time the processing of the collectedframe into a compressed MP3 frame takes. WithMP3, expect an additional processing delayintroduced by the transmitter of roughly 20ms-60ms.Transmission over the network: The block/frame ofsamples now needs to be sent over the network,potentially fighting with other traffic for bandwidth.On a local LAN, the delay will typically be quite low(msecs maybe), but beware .. if there is"sometimes" a fight over bandwidth/buffering in aswitch or router, you may see average very lowdelays but the delay incurred by some packetscould be substantially higher. The differencebetween the fastest and the most delayed packet iscalled "Jitter". For example, if the transmission ofan audio block over the network takes a min. of5ms and in the worst case 200ms, the "jitter" willbe 195ms.Reception at the decoding side: The D/A at the endof the data flow in the decoder must be constantlyfed with samples at the sample rate. As thesamples do not come one-by-one over the network,a buffer is unavoidable.The buffer must be configured to a level which ishigher than the worst jitter so that the D/A endnever runs out of data. It typically makes sense toadd a bit more to the buffer to consequently avoidan "out of samples" situation, as this is an (audible)fault, such as a chirp.With MP3, the decoder processing must take placebetween the network buffer and the D/A. As thedecoding functionality needs to work on the wholeMP3 frame and cannot really start doing this beforeit is delivered complete, the network receivingissue 27_28buffer must contain a full MP3 frame before thedecoding can be started. And as the decodinghappens in "blocks", an output buffer "behind" thedecoder for samples again needs to be established.The last addition of delay is not really necessarytechnology wise, but a fact in Barix devices. We usea Main CPU for network tasks and a DSP driving theD/A, which turns the samples back to analog audio(and has a sample buffer implemented). The DSP isnecessary for MP3 (and AAC etc etc) decoding, forPCM it mainly works as a pass-through. Theinterface between the main CPU and the DSP isquick and does not need much additional buffering,however, the DSP has an input buffer also.DSP Sample buffer: This buffer can introduce asignificant delay for low bitrate/sample ratestreams. Depending on which Barix product youuse, there are different DSPs "under the hood",with different sample/output buffers. As such, theAnnuncicom and Exstreamer 500/1000 devicesproduce a much shorter delay than Exstreamer100/110/200 devices.So, at the end you have several sources introducingdelay, with the buffering for network jitter beingoften the most significant one, but a "base delay",depending on sample rate, encoding format etc isalways present. As you can figure from the aboveexamples, if you have the bandwidth, it often makessense to configure higher sampling rates andbitrate streams, as that will effectively lower thedelay due to the fact that the constant (byte wise)buffers in the chain have a smaller through delay.Overall, with the Exstreamer 1000/500 and theAnnuncicom products, an end-to-end delay ofaround 50ms is currently the lowest. The softwarehas not been optimized for very low delay.However, with optimized software, you can get thedelay down to well below 20ms - that has beenproven in our labs (for a specific project). We are inthe process to bring this number down further,obviously, this can only be done by sending manymore blocks over the network, so you need morebandwidth.By sending samples every 1ms (1000 times persecond !) over the network, delays down to about5ms should be achievable with an optimal networkwith almost no jitter. We are currently testing outwhat is possible in the labs .. so stay tuned !Any IP codec of any manufacturer is bound by theneed for packetizing, and buffering against jitter. Ifyou can show me a device from any manufacturer,which routes Audio over IP, works over a networkwith 50ms jitter, sends less than 100 packets persecond and introduces an end-to-end delay frominput to output of less than 10ms, thismanufacturer has defied physics and i will be happyto buy you a beer and work for them.About Barix AGBarix AG, headquartered in Zurich Switzerland,specializes in research and development of state ofthe art IP based communication and controltechnology. Barix products are stand-alone andable to remotely connect worldwide over standardnetworks / Internet offering new and improvedsolutions to the professional audio distribution,communication and automation industries. Barixproducts provide solutions in audio over IP (audiodistribution and monitoring, communication,security) and automation (remote control,monitoring and maintenance).(www.barix.com )
IPfocusIntroducing STENTOFON AlphaComXE Audio Servers with HD VoiceZenitel, supplier of the STENTOFON® and VINGTOR®brands for audio and security communicationsystems based upon Critical Communication over IP(CCoIP®), announces the advanced STENTOFONAlphaCom XE series of audio servers based uponstate of the art VoIP technology.The new AlphaCom XE is powered by the nextgeneration CCoIP PROCESSOR IP board, providingmore features, greater flexibility and increasedaudio bandwidth. AlphaCom XE utilizes true IPaudio edge devices (IP masters, IP substations andSIP stations) that provide HD Voice, active noisecancellation, adaptive jitter buffering, and anintegrated managed switch with advancednetworking and security functions (VLAN, IEEE802.1X). It offers more capacity than ever, allowingfor additional software based features andfunctions such as PA broadcasting and messagingservices, security voice guidance, internal andexternal networking, call billing, audio conferencingand SIP station support. The XE audio server seriesis backwards compatible providing simple upgradesand expansion of existing AlphaCom systems.AlphaCom XE offers superior audio quality with anew enhanced feature active noise cancellation.Active noise cancellation measures the microphonesignal and calculates noise components in thesignal, removing noise and leaving crystal clearvoice audio. This and many other features such asredundancy and alternative routing makeSTENTOFON the platform of choice for criticalcommunications.The feature rich AlphaCom XE-series audio serverincludes extended integration with CCTV, accesscontrol, alarms, public address, telephony and avariety of features and solutions that can be addedas required. The use of standard IT technologyallows remote programming, logging andmaintenance via AlphaPro, Syslog and standardweb browsers. The AlphaCom XE comes in differentcabinet sizes, depending on the required number oftraditionally wired intercom stations. For an all IPsolution,the new 1 unit XE1 server can control up to552 IP stations, or linked into an AlphaNet ofservers it can provide communication paths formillions of intercom stations globally. The new XE1server is designed to be environmental friendly andhas very low power consumption and weight, andcan be used to support varieties of audio solutionsfor Security Applications, Prisons, Airports, Lifts,Parking, Schools and many more.COMMEND UK Launches New Generation ofIntercom Stations – INTERCOM 2.0Commend UK, has launched its new Intercom 2.0‘Series WS’ range of highly reliable wallmountedIntercom Stations to deliver improved audio andspeech quality, enhanced reliability and a widerrange of solution combinations.Series WS includes a family of innovative vandalresistant Intercom units, which bring together thelatest in sound, vision, control and designtechnology. The units are designed to enhancesafety and security in public places such as lifts, carparks, airports, stations and residential buildings.These can be readily integrated into most existingfire and security systems, including CCTV, accesscontrol, voice, PA and emergency Help Points. Justone CAT 5 cable incorporates voice, video and powerfor ease of installation, and space and energyefficiency.The units operate using Commend’s highly-secureIntercom over Internet Protocol (IoIP®). Its bespokesoftware can be easily configured via IP, meaningthat trained installers can make changes quicklyand remotely.New 16kHz bandwidth means that speech qualityand clarity are assured, even in stringent ambientnoise environments, and certain units include builtincolour video cameras, or TFT monitors to enableoperators to see and hear to whom they are talking.The electronics in the new vandal resistant SeriesWS Intercom stations are protected by a durablehigh-grade steel front plate with such innovationsas ‘poke protection’, special screws to furtherprotect against vandalism and the ability to soundan alarm at the control if the unit is tampered with.All Series WS unit’s are certified to IP 65 (and IK 07for the vandal resistant stations) such thatperformance will not be affected by extremeweather conditions, dirt or dust.The range includes products designed specifically tosuit a variety of purposes. For the healthcare sectorfor example, Commend has designed a membraneprotected wipe down version, for town centres avandal resistant robust station and for residentialproperties the aesthetic, multi-functional rangeincluding an optional handset.Commenting on the newest range, Commend UK’sGreg Gregoriou said: “For us, and for people usingour technology, every word counts – in real time, inexcellent sound quality and across any distance.And thanks to the Series WS range it is set to beheard more directly and more clearly than everbefore.“The range signifies considerable investment, with agreat deal of consideration both for the end userwith an extensive combination of solutions, and alsofor the installer with consistency in design for easeof installation.”issue 27_29
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