FEATURE · STEREO AUDIO · F1
Alternating audio, in true stereo.
Auditory bilateral stimulation with sample-accurate left-right panning, generated on the client's device.
DEFINITION
Stereo audio BLS alternates a tone between the client's left and right ear through the Web Audio API. The therapist controls speed, tone frequency, volume and pan depth in real time.
What it is
A stereo-panned tone that alternates between the left and right ear at a rhythm the therapist sets, providing the auditory dual-attention task used in EMDR.
Why it matters clinically
Auditory BLS is a validated modality within EMDR protocol. It is the modality of choice when eye tracking is fatiguing, when a client prefers to close their eyes, or when combining modalities.
How BilateralSync implements it
The tones are generated on the client's device with the Web Audio API. Pan depth is adjustable from subtle to full stereo. Volume and tone frequency are independently controllable by the therapist and reflect on the client's headphones in real time.
Frequently asked questions
How does stereo audio BLS work in a browser?＋
BilateralSync generates the tones through the Web Audio API directly on the client's device. Panning between the left and right ear is applied client-side, so audio latency is essentially the latency of the client's own audio subsystem — not the network.
Do clients need headphones?＋
Yes. Stereo panning depends on the left and right channels reaching the ears separately, which speakers do not reliably deliver. Any wired or wireless stereo headphones work.
Can I use stereo audio and visual BLS together?＋
Yes. Visual and auditory stimulation run in perfect sync so the therapist can combine modalities in a single set.
Related reading
Bilateral Stimulation
Auditory Bilateral Stimulation
Auditory bilateral stimulation uses tones alternating between the left and right ear. Learn how stereo BLS is used in EMDR and how to configure it online.
Bilateral Stimulation
Bilateral Stimulation Music
How bilateral stimulation music and stereo-panned tones work in EMDR. Evidence, use cases and how to deliver auditory BLS reliably online.
Theory & Research
How Bilateral Stimulation Works
How does bilateral stimulation work in EMDR? A clear overview of working-memory theory, orienting response and current evidence for the mechanism of BLS.