A greeting that plays perfectly on your laptop is refused by the phone system, with an error that explains nothing. The file is fine. It is just not the shape a phone line carries, and the importer will not reshape it for you.
Your file stays in your browser. Nothing is uploaded.
Each preset comes from that vendor's own page. The page below cites every one.
Presets, and where each one comes from
Every preset below was read off the vendor's own documentation on the date shown, and a vendor whose page could not be read is not in the table. If your system is missing, the first row is the safe answer: 8 kHz, one channel, 16-bit PCM in a WAV file is what most importers accept.
| System | Rate | Channels | Encoding | File | Also accepts | Source |
|---|---|---|---|---|---|---|
| Any phone system | 8 kHz | 1 | 16-bit PCM | WAV | Not stated | Media Streams WebSocket messages, Twilio Read 2026-09-06 |
| Ringfully | 8 kHz | 1 | 16-bit PCM | WAV | MP3 | Play, TwiML for Programmable Voice, Twilio Read 2026-09-06 |
| Twilio, Play verb | 8 kHz | 1 | 16-bit PCM | WAV | MP3, AIFF, GSM, mu-law | Play, TwiML for Programmable Voice, Twilio Read 2026-09-06 |
| Twilio, Media Streams | 8 kHz | 1 | mu-law (G.711) | No header | Not stated | Media Streams WebSocket messages, Twilio Read 2026-09-06 |
| Yeastar, P-Series | 8 kHz | 1 | 16-bit PCM | WAV | MP3, GSM, A-law WAV, mu-law WAV | Requirements of custom audio files, Yeastar P-Series Read 2026-09-06 |
| Grandstream, UCM series | 8 kHz | 1 | 16-bit PCM | WAV | GSM, A-law, mu-law | Voice prompt customization, Grandstream Documentation Center Read 2026-09-06 |
| Cisco, Unity Connection | 8 kHz | 1 | mu-law (G.711) | WAV | PCM linear, A-law, G.729a, G.726, GSM 06.10 | Media player in the Messaging Assistant web tool, Cisco Unity Connection 12.x Read 2026-09-06 |
Vendors we could not read a format for are left out rather than guessed at, which is why some well-known systems are missing. Formats change, and a date on a row is the last time somebody checked it. If a row here disagrees with your vendor today, believe your vendor, and tell us so we can fix it.
How it works underneath
A phone call is sampled eight thousand times a second on one channel. That is the G.711 standard the network runs on, and it is why a phone call sounds like a phone call. Everything above that band is discarded before your caller hears it, so uploading a 44.1 kHz stereo master gains nothing and gives the importer something to refuse.
The three encodings are three ways of writing those samples. 16-bit PCM writes each one as two bytes, plainly. Mu-law and A-law are companded: each sample becomes one byte, with the quiet parts given more resolution than the loud ones, which is why they sound better than an 8-bit PCM file of the same size. Mu-law is the North American and Japanese variant, A-law the international one.
A WAV file is a header saying which of those it is, followed by the samples. Some systems want the header, and one on the list wants the samples with no header at all, because it is reading them off a live stream rather than opening a file.
This page does that work in the browser. The recording is decoded by the browser itself, mixed to one channel, resampled by the browser's own audio engine, and written back out by about a hundred and fifty lines of our own code. There is no endpoint behind this page and no request leaves it, which is also why it costs nothing to run and why your caller's voice stays your business.
Questions
Why does my phone system refuse a file that plays fine on my computer?
Because the two are checking different things. Your computer plays almost anything. A phone system's importer checks the sample rate, the channel count and the encoding against what it can put on a call, and refuses anything else rather than guess. A 44.1 kHz stereo MP3 from a phone or a voice-over studio fails that check even though the recording is perfect.
Will 8 kHz mono make my greeting sound worse?
It will sound the same as it does on a phone call, which is the only place it is going to be heard. A phone line carries 8 kHz of one channel, so the detail above that is discarded somewhere no matter what you upload. Converting first means you hear what your callers will hear before you commit to it.
What is the difference between PCM, mu-law and A-law?
They are three ways of writing the same 8 kHz sound. PCM at 16 bits is the plain one and the largest. Mu-law and A-law are the G.711 codecs a phone network uses; each sample is one byte instead of two, so the file is half the size. Mu-law is used in North America and Japan, A-law in most of the rest of the world. Use whichever your vendor's page asks for.
Do you keep my file?
No. Your file is read, converted and offered back to you inside your own browser tab. It is never sent to Ringfully or to anybody else, there is no upload, and closing the tab is all it takes to be rid of it.
Once the file is right
The file is one step. What plays it is your phone menu: the greeting, the options, the hours behind them, and what happens at four in the afternoon on a holiday. That is a thing you should be able to change yourself, in a browser, in two minutes.