> ## Documentation Index > Fetch the complete documentation index at: https://docs.getrivet.ca/llms.txt > Use this file to discover all available pages before exploring further. # Auditory bilateral stimulation > Eight sound presets, and why the tone is in the ear the stimulus is on rather than merely moving at the same rate. The audio modality is enabled by default in EMDR 2.0 (the de Jongh / Matthijssen protocol expects multimodal stimulation) and disabled in Classic EMDR. When it's on, your client hears a tone that travels between their ears with the stimulus. The tone is made on the spot rather than played back. Nothing is downloaded and there's no audio file anywhere in the session. ## The eight sound presets | Preset | Character | Notes | | -------------- | --------------------- | ------------------------------------------------------------------------------------------------------------------------ | | **Sine** | Pure carrier tone | Classic EMDR default. The cleanest, most neutral sound — what in-office EMDR hardware kits (EMDR Kit, NeuroTek) produce. | | **Triangle** | Softer than sine | A warmer harmonic content than sine; less sterile feel without losing clarity. | | **Soft drum** | Subtle thump | EMDR 2.0 default. Sine carrier with a fast envelope shaping — a percussive but gentle texture. | | **Chime** | Bell-like decay | Triangle waveform with a slower envelope; a tone that lingers slightly between pans. | | **Click** | Very short ping | A sharp attack with minimal sustain — closest to the in-office BLS device "click." | | **Woodblock** | Percussive | Square waveform with a fast envelope; firmer than soft drum. | | **Alpha drum** | Meditative pulse | Low triangle with a slow envelope; a deeper, more grounding texture. | | **Tick** | Metronome-tight click | Sawtooth waveform with an ultra-fast envelope; precision feel. | Each preset shapes the **timbre and attack** of the tone — the underlying carrier frequency and the pan rate are independent controls. ## Carrier frequency The frequency slider is set to **250 Hz** by default and clamped to **200 to 450 Hz**. This is the pitch of the carrier tone underneath whatever preset you've chosen. Most clients tolerate the 200–300 Hz range well — high enough to be clearly audible without being shrill, low enough to feel grounded. Move higher (350–450 Hz) for clients who prefer a brighter feel; move lower for clients who report the higher range as fatiguing. ## Where the tone sits The tone isn't matched to the movement — it *is* the movement. Where the stimulus sits on its path and which ear the tone is in are the same value, worked out once and used for both. There's no second clock keeping the sound in step with the picture, so the tone can't slide behind the stimulus over a long set and can't drift when you change the speed partway through. That matters because you can't hear your client's audio from your side of the screen. If a tone lagged the stimulus, nothing on your side would tell you. See [One movement, not three](/emdr/staying-in-sync). Hard panning is intentional. This is **not binaural beats** — binaural beats use two slightly detuned tones in different ears and are a different mechanism (entrainment) not validated for EMDR. Rivet's audio modality is straight stereo panning of a single tone, matching the in-office BLS hardware convention. ## Volume A 0 to 100% slider. The default is 60%. The client's device volume sits on top of this — a 60% Rivet volume with the client's phone muted produces no sound. If the client reports they can't hear the audio, ask them to check their device volume first. ## iOS Safari handling iOS Safari blocks audio playback until the user makes a gesture. Rivet sets up the audio at the moment the client taps Join — granting camera and mic permission counts as the gesture — so audio just works when BLS starts. This was historically the #1 BLS support category across the industry. Rivet sidesteps it by setting up the audio at the moment the client taps Join, not when BLS starts. ## When the audio stops The tone stops when the set stops and when the session ends. Nothing keeps playing in the background afterwards — there's no version of this where your client is still hearing the tone once you've both left. ## Headphones vs speakers For optimal BLS, the client should use **stereo headphones**. Earbuds work. Laptop speakers technically work but the L↔R panning is far less distinct when both speakers are 6 inches apart, and phone speakers (single mono output) lose the bilateral effect entirely. In your reminder email or pre-session message, suggest the client have headphones or earbuds ready. See [Best practices for virtual EMDR](/emdr/best-practices-for-virtual-emdr). ## Related articles The visual modality — stimulus shapes, motion paths, and the 0.3 to 2.0 Hz speed range. Headphones, browser window, client environment, and choosing modalities for a given client. The Configure modal walkthrough — including the modality picker and sound preset row.