VMS to SLN Converter

Get your VMS recordings into SLN format effortlessly

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Broader Reach

VMS recordings become far more usable as SLN. The conversion unlocks raw signed linear audio that VMS cannot provide.

Speedy Output

Speed matters. Our converter transforms VMS to SLN in moments, so you get your audio in the right format without waiting.

Universal Access

No platform restrictions. Convert your VMS audio to SLN on any operating system through a standard web browser.

How to convert VMS to SLN

1

Select files from Computer, Google Drive, Dropbox, URL or by dragging it on the page.

2

Choose sln or any other format you need as a result (more than 200 formats supported)

3

Let the file convert and you can download your sln file right afterwards

About formats

VMS (Voice Messaging System) is a compressed audio format designed for telephony and voice mail applications, originally used in Germany. Files with the .vms extension encode spoken audio using Continuously Variable Slope Delta modulation (CVSD), a method suited to low-bandwidth voice transmission over telephone networks. The format operates at 8 kHz, matching the standard digital telephony sampling frequency, and produces self-describing files that embed encoding parameters within a short header. This header distinguishes VMS from raw CVSD streams, letting playback tools process recordings without external configuration. The SoX audio toolkit provides native read and write support, making it straightforward to convert VMS recordings into WAV or other modern formats. A practical advantage is the format's small file size — CVSD compression keeps voice mail messages compact enough for systems with limited disk capacity, which was critical in early telephony infrastructure. The encoding degrades gracefully under noisy channel conditions, preserving speech intelligibility even when errors occur. Although VMS has been superseded by modern codecs in current voice messaging platforms, it remains relevant for recovering legacy voice mail archives.
Developer: SoX Contributors
Initial release: 1991
SLN (Signed Linear) is a headerless raw audio format storing 16-bit signed linear PCM samples at 8000 Hz mono, most closely associated with Asterisk — the open-source PBX framework developed by Digium (now Sangoma Technologies). Within Asterisk, SLN serves as the native internal audio representation: every codec transcoding operation passes through signed linear as an intermediate step. This makes SLN the backbone of Asterisk's codec translation architecture. The format contains nothing but raw samples — no headers, no metadata, no framing — so parameters must be known in advance. While this lack of self-description might seem limiting, it is actually an advantage in telephony where sample format is fixed by convention and every overhead byte matters across thousands of simultaneous channels. The 8000 Hz rate aligns with the G.711 standard for traditional telephony, capturing the full 300-3400 Hz voice band. Asterisk also supports extended variants (sln16, sln32, sln48) for wideband audio. SLN files require no decoding — just direct memory mapping — making them ideal for real-time mixing, conferencing, and prompt playback in high-density VoIP environments.
Initial release: 1999

Frequently Asked Questions

What makes SLN a better choice than VMS?

VMS suffers from German voice mail standard unsupported by modern players. SLN offers VoIP system integration.

What can I use to play SLN?

You can open SLN with Asterisk PBX, SoX, and VoIP telephony systems.

Is there quality loss from VMS to SLN?

No quality is lost. SLN stores audio without additional compression, so your VMS recording carries over at full original fidelity.

Can I do this conversion from my phone?

Yes. The online converter is platform-independent — use it from any computer, tablet, or smartphone with a web browser.

Are there limits on VMS to SLN conversion?

Standard conversions work without restrictions for typical use. Premium plans provide additional speed and capacity for large workloads.

Is registration needed for this conversion?

No account is needed for standard conversions. Simply upload your VMS recording, choose SLN, and download the result.