What audio format do 3CX phone systems (PBX) require?
3CX describes itself as an enterprise phone system, hosted in the cloud or self-managed so you keep control of your own trunks and numbers, and calls the wider product a complete communications platform. In practice that means one system handling calls, the web client, apps and the contact centre features, and it is the same system that plays your recorded prompts to every caller. The current major release line is V20.
3CX documents the requirement plainly. Prompts must be WAV, mono, 8 kHz, 16 bit, and that applies to IVR prompts, queue announcements and custom system prompt sets alike. Anything else has to be converted before it will work properly, and 3CX provides both an online converter and instructions for doing it in Audacity.
So the specification is not the hard part. The hard part is that converting a file into the right format does nothing whatsoever to make it sound good. A recording made on a laptop in an open-plan office is still a recording made on a laptop in an open-plan office after it has been resampled to 8 kHz. If anything the conversion exposes it, because 8 kHz throws away everything above roughly 4 kHz, and what survives is the middle of the sound where room tone, mouth noise and desk rumble all live.
The specification
3CX prompt format
- Container: WAV
- Channels: mono
- Sample rate: 8 kHz
- Bit depth: 16 bit
Applies to IVR prompts, queue announcements and custom system prompt sets.
Why you record at 48 kHz and deliver at 8 kHz
It seems logical to record at the sample rate the system wants. It is the wrong way round. You record at full quality, master the audio knowing where it is going, and convert down as the last step.
Mastering for telephony is a real process and it is the difference between prompts that sound like a company and prompts that sound like a voicemail. It means shaping the EQ for a band that stops around 4 kHz, so the read still has presence when the top has been removed. It means controlling sibilance, because an S that was crisp at full bandwidth turns into a hiss once the frequencies around it are gone. It means compression set for the playback range rather than for headphones, so the quiet parts survive a noisy car and the loud parts do not distort on a cheap handset. And it means setting a consistent level across every prompt, so callers are not adjusting the volume between the greeting and the queue message.
Keeping the full-quality master matters for a second reason. The same lines are often wanted later on the website, in an app, in a video or on a smart speaker, and a file that has already been reduced to 8 kHz cannot be rescued. Record once, keep the master, deploy everywhere.
What to record for a 3CX deployment
Most 3CX installs go live with a greeting and a menu, then accumulate gaps that get filled badly over the following two years. Record the whole set at once. The extra prompts add minutes to a session, and they save you a re-book and a mismatched voice later.
- Main greeting for the digital receptionist, with a separate variant for each trading name if you use more than one.
- Menu options, ideally kept to four or five, with the action before the number.
- Invalid entry and timeout reprompts, which callers hear at their most irritated and which are almost always left as the default system voice.
- Queue announcements, including the initial message and any comfort messages that repeat.
- Music on hold beds, with the voice sitting over them at a level that does not fight the music.
- Out of hours, plus a separate lunchtime or early-close version if you use one.
- Holiday and bank holiday closures, recorded in advance rather than the afternoon before.
- Voicemail greetings, both the general one and the departmental ones.
- Service status messages for outages, so you are not recording under pressure on the day.
The last one is worth dwelling on. The day you actually need an outage message is the day nobody has time to make a good one, which is why so many companies have a stressed manager’s mobile recording sitting on the front of their phone system during their worst week of the year.
Naming files so the upload is boring
3CX deployments get administered by whoever is free, sometimes years after the prompts were recorded. Files called final_v3_NEW.wav are how a menu ends up playing the wrong message.
Name every file for what it does and where it goes, agree the convention before recording rather than after, and keep the same convention for the masters. When we deliver a set we name the files to whatever convention your admin tool or your MSP expects, so uploading is a matter of matching names rather than listening to nine files to work out which is which.
Multi-language prompt sets
3CX supports custom system prompt sets, which is what you need if callers should hear the whole journey in their own language rather than an English menu with one translated line bolted on.
The thing that catches people out is tone matching. If the English voice is warm and the German voice is formal, callers on the German line get a different company. Prompt sets are worth casting together, from one brief, so the personality survives the language change. Script length shifts too, and a menu that fits comfortably in English can overrun once translated.
The problem nobody plans for: changes
Phone menus change. A department moves, an option is added, the opening hours shift. If the original voice is not available, or is available but recording somewhere else on a different microphone, the new prompt does not match. Callers hear the seam even if they could not tell you what they are hearing.
The fix is to arrange it at the start. Our IVR voices hold a long-term retainer on their prompts, recorded on the same microphone in the same chain, so a single line added in two years’ time sits inside the set instead of next to it. It costs far less than re-recording a full menu, which is the usual alternative once the mismatch becomes obvious.
For MSPs and resellers
White-labelled prompt sets
If you install and manage 3CX for clients, we supply prompts in the format and naming you already use, ready to drop in. One point of contact, no client-facing branding from us unless you want it.
Getting it done
Send the prompt list and tell us it is 3CX. We record, master for telephony, convert to WAV mono 8 kHz 16 bit, name the files to your convention and hand over the full-quality masters alongside. If the script needs tidying first, we will do that too. Details on our IVR voice recording page, and if you have not settled on a voice yet, start with how to choose a voice for your phone system.
