Why a recording plays back silent and how to fix it

A VICIdial Call recording that plays back as silence is more confusing than a missing recording — the file exists, the Admin search finds it, but playback is blank. The file contains audio data, just no actual voice. There are four common reasons this happens.

Reason 1: No audio path reached MixMonitor

MixMonitor mixes the audio streams it sees on the Asterisk channel at the moment it starts. If the Agent leg and the customer leg are bridged but one side's audio never flows through the same Asterisk server where MixMonitor is running, that side records as silence. This most often happens in multi-server clusters where the call was answered on Server A but an AGI (Asterisk Gateway Interface) script or dialplan transfer moved the bridge to Server B while MixMonitor kept running on Server A. The fix is to ensure recording starts after the final bridge is established, or to use a dedicated recording gateway server.

Reason 2: DTMF muting stayed active

The DTMF muting feature in VICIdial mutes the recording for a configurable number of seconds after it detects a DTMF tone. This is designed for PCI compliance — muting card numbers entered by keypad. If Recording DTMF Muting is set to a high value (say, 60 seconds) and a DTMF tone fires early in the call, a significant portion of the conversation records as silence. Check the Recording DTMF Muting field on the campaign. If it is non-zero and you do not need PCI card muting, set it to 0.

**Heads up:** When Recording DTMF Muting is enabled on a campaign, the Mute Recording Button is automatically disabled. You cannot have both active at once. If you switched from DTMF muting to the manual mute button approach, confirm that the DTMF muting value is set back to 0, otherwise the DTMF detector will still suppress audio.

Reason 3: Mute Recording Button was left active

If the Mute Recording Button is enabled on the campaign and an agent clicked it but never clicked it again to resume, the recording runs for the rest of the call with silence on the muted side. The campaign setting is Mute Recording Button = Y, which adds the mute control to the agent screen. Agents should be trained that leaving the mute active for more than 15 minutes (the recommended maximum) and forgetting to un-mute creates silent recordings that are useless for quality review.

Reason 4: Stereo channel set to wrong mode

The Stereo recording Stereo Call Recordings setting has four values: DISABLED, CUSTOMER_ONLY (agent side is silent), CUSTOMER_MUTE (customer side is silent), and BOTH_CHANNELS. If you open the stereo file from a call and hear only one channel or silence on one channel, check this setting. CUSTOMER_ONLY is a valid choice for some compliance uses — the customer voice is captured but the agent is not. If that is not what you intended, switch to BOTH_CHANNELS.

Reason 5: Codec mismatch causing unreadable audio

A recording that plays as silence (or as noise) in a browser player but sounds fine in a desktop audio tool is usually a Codec mismatch. GSM-format recordings need to be decoded before many web players can handle them. If your Admin UI plays the file through a browser audio element without transcoding, GSM files will appear silent. The fix is to convert recordings to WAV at download time, or switch the Campaign Rec extension from 8310 (GSM) to 8309 (WAV) so files play natively.

flowchart TD
  A[Recording plays silent] --> B{DTMF muting enabled?}
  B -->|Yes - high value| C[Lower DTMF Muting to 0 if not needed]
  B -->|No| D{Mute button left active?}
  D -->|Yes| E[Train agents - retrain workflow]
  D -->|No| F{Stereo mode correct?}
  F -->|Wrong channel mode| G[Set to BOTH_CHANNELS]
  F -->|Correct| H{Multi-server bridge issue?}
  H -->|Yes| I[Start recording after final bridge]
  H -->|No| J{Codec mismatch in player?}
  J -->|Yes| K[Transcode GSM to WAV for playback]

Quick diagnostic steps

• Play the raw file with a local audio tool (Audacity, VLC) — if audio exists there but not in the browser, it is a codec/player issue
• Check Campaign Recording DTMF Muting — if non-zero and you do not need PCI muting, set to 0
• Review the Stereo Call Recordings setting — CUSTOMER_ONLY means the agent channel is intentionally silent
• On multi-server clusters, confirm MixMonitor is starting on the same server that holds the bridged audio
• Check the Recording format (WAV/MP3) (8309 vs 8310) and whether your playback player can decode GSM natively

For a full picture of how recording modes and extensions work, read VICIdial call recording explained. If the recording file does not exist at all rather than playing silent, see fix VICIdial missing recordings. Want a managed VICIdial platform where recording configuration is validated at setup? See VICIfast pricing.