VOS3000 IVR Codec Priority: Advanced Voice Prompt Encoding Configuration
When your VOS3000 IVR system plays a voice prompt to a caller, which audio codec does it use? Does it match the caller’s codec, or does it force a specific encoding? The answer is controlled by the VOS3000 IVR codec priority parameter — IVR_CODEC_PRIORITY — which determines the order in which the IVR negotiates codecs for voice prompt playback. Getting this setting right is critical: a mismatched codec forces the softswitch to transcode, consuming CPU resources and potentially degrading voice quality.
According to the official VOS3000 V2.1.9.07 Manual, Section 4.3.5.3 (Audio Service Parameter), the IVR_CODEC_PRIORITY parameter has a default value of “g729a,g729,g723,g711a,g711u” and is described as “Voice Codecs Priority (g729a,g729,g723,g711a,g711u).” This comma-separated list defines the order in which the IVR attempts to negotiate codecs with the calling endpoint.
All data in this guide is sourced exclusively from the official VOS3000 V2.1.9.07 Manual, Section 4.3.5.3 — no fabricated values, no guesswork. For expert assistance with your VOS3000 deployment, contact us on WhatsApp at +8801911119966.
Table of ContentsVOS3000 IVR Codec Priority: Advanced Voice Prompt Encoding Configuration What Is VOS3000 IVR Codec Priority? Why VOS3000 IVR Codec Priority Matters Supported IVR Codecs — Complete Reference (VOS3000 IVR Codec Priority) Codec Priority — Deployment Scenarios (VOS3000 IVR Codec Priority) Common VOS3000 IVR Codec Priority Problems and Solutions Problem 1: IVR Voice Prompts Sound Distorted Problem 2: IVR Prompts Not Playing — No Audio Problem 3: High CPU Usage on VOS3000 Server VOS3000 IVR Codec Priority Configuration Checklist Frequently Asked Questions What is VOS3000 IVR codec priority? What is the default IVR_CODEC_PRIORITY? Why should I match the IVR codec to the endpoint codec? Can I add codecs not listed in the default priority? What is IVR_WEB_CALLBACK_SAME_TIME_CODEC? How do I change the IVR codec priority in VOS3000? Need Professional VOS3000 Setup Support?
What Is VOS3000 IVR Codec Priority?
The VOS3000 IVR codec priority is a parameter that determines the order in which the IVR module negotiates audio codecs during call setup. When the IVR needs to play a voice prompt (such as a balance announcement, IVR menu, or voicemail greeting), it must establish a media stream with the calling endpoint using a mutually supported codec. The IVR_CODEC_PRIORITY parameter tells the IVR which codec to try first, second, third, and so on.
According to the official VOS3000 V2.1.9.07 Manual, Section 4.3.5.3:
AttributeValue ParameterIVR_CODEC_PRIORITY Default Valueg729a,g729,g723,g711a,g711u DescriptionVoice Codecs Priority (g729a,g729,g723,g711a,g711u) LocationOperation management → Softswitch management → Additional settings → Audio service parameter
Key insight: The default priority order places G.729A first — a low-bandwidth codec that uses only 8 kbps. This makes sense for IVR scenarios where bandwidth efficiency is prioritized and the audio content (voice prompts) is pre-recorded and can be encoded in any supported format. The manual explicitly lists the supported codecs in the parameter description: g729a, g729, g723, g711a, g711u. Only these five codecs are available for IVR codec priority configuration.
Why VOS3000 IVR Codec Priority Matters
Incorrect codec priority configuration causes several problems:
Transcoding overhead: If the IVR selects a codec different from what the endpoint is using, the softswitch must transcode the audio in real time — consuming CPU resources and adding latency
Voice quality degradation: Transcoding between compressed codecs (e.g., G.729 to G.711 and back to G.729) introduces cumulative quality loss — the audio sounds robotic or distorted
Resource waste: Each transcoding session consumes DSP or CPU capacity — in high-concurrency IVR deployments, excessive transcoding can exhaust system resources
Bandwidth mismatch: If the IVR forces a high-bandwidth codec (G.711) when a low-bandwidth codec (G.729) would suffice, unnecessary bandwidth is consumed on the IVR media path
Negotiation failures: If the IVR and endpoint have no common codec in their supported lists, the call cannot establish a media stream — the IVR prompt will not play
Supported IVR Codecs — Complete Reference (VOS3000 IVR Codec Priority)
The VOS3000 IVR codec priority supports five codecs, each with different characteristics. Understanding these codecs is essential for proper priority configuration:
CodecBitrateQualityBest For g729a8 kbpsGood (compressed)Bandwidth-efficient IVR; default first choice; Annex A variant g7298 kbpsGood (compressed)Standard G.729 without Annex A; compatible with most endpoints g7235.3/6.3 kbpsFair (highly compressed)Low-bandwidth links; minimal bandwidth consumption g711a64 kbpsExcellent (uncompressed)High-quality IVR prompts; A-law standard (Europe/international) g711u64 kbpsExcellent (uncompressed)High-quality IVR prompts; u-law standard (North America/Japan)
Codec selection principle: The IVR should ideally use the same codec as the calling endpoint. This eliminates transcoding entirely — the voice prompt audio is simply passed through in the same encoding. To achieve this, list the most commonly used codecs first in the priority list, matching your endpoint population’s typical codec preferences. For help with codec configuration, reach us on WhatsApp at +8801911119966.
Codec Priority — Deployment Scenarios (VOS3000 IVR Codec Priority)
Different deployment scenarios benefit from different codec priority orders:
ScenarioRecommended PriorityRationale Wholesale carrier (G.729 endpoints)g729a,g729,g723,g711a,g711u (default)Most endpoints use G.729; bandwidth efficiency is paramount Enterprise SIP phones (G.711)g711a,g711u,g729a,g729,g723Desktop SIP phones typically use G.711; prioritize for zero-transcoding Mixed environmentg729a,g711a,g711u,g729,g723Balance between bandwidth savings (G.729) and quality (G.711) North America deploymentg711u,g729a,g729,g723,g711aG.711 u-law is the North American standard; prioritize it first European deploymentg711a,g729a,g729,g723,g711uG.711 A-law is the European standard; prioritize it first
Related parameter: The manual also lists IVR_WEB_CALLBACK_SAME_TIME_CODEC with a default of “g729a” — described as “Codec for Call Both Side.” This parameter specifically controls the codec used when both sides of a callback call use the same codec simultaneously. For more on codec configuration, see our VOS3000 parameter description guide.
Common VOS3000 IVR Codec Priority Problems and Solutions
Problem 1: IVR Voice Prompts Sound Distorted
Symptom: When callers reach the IVR menu, the voice prompts sound robotic, garbled, or have audible artifacts.
Cause: The IVR is using a compressed codec (G.729 or G.723) while the endpoint is using G.711, forcing the softswitch to transcode. Double transcoding (G.711 → G.729 → G.711) degrades quality.
Solutions:
Move G.711 codecs higher in the IVR_CODEC_PRIORITY list if endpoints primarily use G.711
Pre-encode IVR voice prompts in the same codec as the most common endpoint codec
Check if the voice prompt source files are high quality (16-bit PCM, 8kHz) before encoding
Problem 2: IVR Prompts Not Playing — No Audio
Symptom: The IVR call connects but no voice prompt audio is heard — the caller hears silence.
Cause: The IVR and endpoint failed to negotiate a common codec — there is no mutually supported codec in the SDP negotiation.
Solutions:
Verify IVR_CODEC_PRIORITY includes all five supported codecs
Check the endpoint’s supported codec list — ensure at least one codec overlaps with IVR’s list
Test with a different endpoint that supports more codecs
Problem 3: High CPU Usage on VOS3000 Server
Symptom: The VOS3000 server shows high CPU utilization, especially during peak IVR call volume.
Cause: Excessive transcoding between IVR codec and endpoint codec is consuming significant CPU resources on every IVR call.
Solutions:
Reorder IVR_CODEC_PRIORITY to match the most common endpoint codec — eliminate transcoding where possible
Monitor the number of transcoding sessions and compare to total IVR call count
Consider standardizing endpoint codec configuration to match IVR_CODEC_PRIORITY
VOS3000 IVR Codec Priority Configuration Checklist
CheckActionStatus 1Identify the most common codec used by your endpoints (G.729 or G.711)☐ 2Set IVR_CODEC_PRIORITY to list the most common endpoint codec first☐ 3Ensure voice prompt audio files are encoded in the first-priority codec☐ 4Test IVR calls and verify no transcoding occurs (check SIP SDP negotiation)☐ 5Monitor CPU usage and voice quality — adjust priority if transcoding is detected☐
For expert guidance on VOS3000 IVR codec configuration, reach us on WhatsApp at +8801911119966.
Frequently Asked Questions
What is VOS3000 IVR codec priority?
VOS3000 IVR codec priority is the parameter IVR_CODEC_PRIORITY that determines the order in which the IVR negotiates audio codecs during call setup. According to the VOS3000 V2.1.9.07 Manual (Section 4.3.5.3), the default is “g729a,g729,g723,g711a,g711u” — the IVR tries G.729A first, then G.729, G.723, G.711 A-law, and finally G.711 u-law. The parameter supports five codecs and defines the negotiation priority order. Matching the IVR codec to the endpoint codec avoids transcoding, which saves CPU resources and preserves voice quality.
What is the default IVR_CODEC_PRIORITY?
The default IVR_CODEC_PRIORITY is g729a,g729,g723,g711a,g711u according to the VOS3000 V2.1.9.07 Manual (Section 4.3.5.3). This order prioritizes bandwidth-efficient codecs (G.729A at 8 kbps) over high-quality codecs (G.711 at 64 kbps). The default is well-suited for wholesale VoIP deployments where bandwidth conservation is important. If your endpoints primarily use G.711 (e.g., enterprise SIP phones), consider reordering the priority to place g711a or g711u first.
Why should I match the IVR codec to the endpoint codec?
When the IVR and endpoint use the same codec, no transcoding is required — the voice prompt audio is passed through directly in the same encoding. Transcoding (converting between codecs) consumes CPU resources on the VOS3000 server, adds latency, and degrades voice quality — especially when double-transcoding occurs (e.g., G.711 endpoint G.729 IVR, requiring conversion in both directions). By matching the IVR codec to the most common endpoint codec, you eliminate transcoding overhead entirely.
Can I add codecs not listed in the default priority?
The VOS3000 manual explicitly lists the supported codecs for IVR_CODEC_PRIORITY as: g729a, g729, g723, g711a, g711u. These are the five codecs supported by the IVR module for voice prompt playback. Adding codecs not in this list (such as GSM, iLBC, or Opus) is not supported by the IVR_CODEC_PRIORITY parameter. Only the five listed codecs can be included in the priority configuration. If your endpoints use other codecs, the VOS3000 softswitch will transcode between the endpoint codec and the IVR’s selected codec.
What is IVR_WEB_CALLBACK_SAME_TIME_CODEC?
According to the VOS3000 V2.1.9.07 Manual (Section 4.3.5.3), IVR_WEB_CALLBACK_SAME_TIME_CODEC has a default of “g729a” and is described as “Codec for Call Both Side.” This parameter specifically controls the codec used when both parties of a callback call use the same codec simultaneously. While IVR_CODEC_PRIORITY controls the general codec negotiation order, this parameter provides a specific override for the simultaneous-call codec scenario. For more on IVR callback parameters, see our callback timing guide.
How do I change the IVR codec priority in VOS3000?
To change the IVR codec priority: (1) Log in to VOS3000 Client, (2) Navigate to Operation management → Softswitch management → Additional settings → Audio service parameter (Section 4.3.5.3), (3) Locate IVR_CODEC_PRIORITY, (4) Edit the comma-separated codec list to reflect your desired priority order (e.g., “g711a,g711u,g729a,g729,g723” for G.711-first deployments), (5) Save and apply the changes. After saving, new IVR calls will use the updated codec negotiation order. Existing calls are not affected.
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