At a Glance

If you are joining a Remoto Playback session from a web browser, iPhone, iPad, or Apple TV and the host is streaming surround sound (5.1 or 7.1), you will automatically hear a stereo version of the mix. Dialogue, music, and effects are all preserved. Surrounds are blended into Left and Right, and the subwoofer channel is removed. No setup is required on your end. If you need the full surround mix, use the Desktop application with a multichannel audio output device.

Overview

When a Remoto Playback session is configured to stream multichannel audio (5.1, 7.1, or up to 16 discrete channels), participants who are monitoring on a stereo device, or who explicitly select stereo output, will hear a fold down (also called a downmix) of the multichannel stream into two channels (Left and Right).

This article explains:

• What a fold down is and why it happens
• How Remoto performs the fold down on each client platform
• The exact fold down coefficients used
• What production teams should keep in mind

Note on Streaming Type: Sessions can be configured as either Desktop Only or Desktop & Web. This setting controls which clients can join the session. It does not change how the fold down works. In a "Desktop Only" session, only Desktop app users participate, so the fold down only applies if a Desktop user selects stereo output. In a "Desktop & Web" session, web, iOS, and Apple TV guests can also join and will automatically receive the stereo fold down described in this article.

What Is a Fold Down?

A fold down is the process of combining a multichannel audio signal (for example, 5.1 surround with six discrete channels) into a signal with fewer channels (typically stereo). The goal is to preserve the spatial intent of the original mix as faithfully as possible, while ensuring all content (dialogue, music, effects, surrounds) remains audible in the reduced channel count.

The standard fold down formula for 5.1-to-stereo is defined by ITU-R BS.775-1 and has been widely adopted across broadcast, cinema, and streaming.

Supported Audio Input Modes

The Remoto host (Desktop application) can configure a session with any of the following audio input modes. The input mode defines the channel layout and ordering, and this is critical because the fold down matrix must know which channel is which.

Important: The distinction between Film, DCP, and SMPTE orderings affects where the Center, LFE, and Surround channels sit in the stream. The fold down engine must respect this ordering to avoid misassigning channels (for example, treating LFE as a Center channel).

Fold Down Coefficients

Standard 5.1 to Stereo (Lo/Ro), ITU-R BS.775-1

This is the reference fold down used across all Remoto clients. Coefficients are expressed in both linear gain and dB:

Resulting formula:

L_out = L + (C × 0.707) + (Ls × 0.707)
R_out = R + (C × 0.707) + (Rs × 0.707)

Note on LFE: The LFE (Low Frequency Effects / ".1") channel is discarded in the standard Lo/Ro fold down per ITU-R BS.775. This is intentional. The LFE carries content meant for subwoofers at +10 dB relative to main channels. Mixing it in at full or even attenuated level into stereo speakers can cause distortion, bass overload, and an unnatural tonal balance. This is standard practice across all professional broadcast and streaming platforms.

Standard 7.1 to Stereo (Lo/Ro)

Extends the 5.1 matrix with the rear surround pair:

Resulting formula:

L_out = L + (C × 0.707) + (Ls × 0.707) + (Lrs × 0.707)
R_out = R + (C × 0.707) + (Rs × 0.707) + (Rrs × 0.707)

Alternative Coefficients (Lt/Rt, Dolby Pro Logic Compatible)

Some playback systems may use the Lt/Rt (Left-total/Right-total) matrix, which preserves surround encoding for downstream Pro Logic decoding. This is not currently used by Remoto's default fold down, but is worth noting for production teams:

The Lt/Rt matrix is not currently used by Remoto's live streaming fold down.

Discrete 16-Channel Streams

When the session is configured as 16 Unrelated (16 discrete channels with no defined spatial relationship), a standard surround fold down matrix does not apply. In this scenario:

• Playback for Web / iOS / Apple TV: Receive a stereo stream from the server. The server-side Opus encoder applies its default channel coupling, which typically sums all channels equally into L/R with gain normalization. This is a lossy simplification and is not meant to represent a meaningful stereo fold.
• Desktop App: Can route individual discrete channels to specific output pairs. When stereo output is selected, the behavior depends on the host's routing configuration. If no custom routing is defined, the first two channels are passed through as L/R.

How Each Client Handles the Fold Down

Playback for Web (Browser)

Desktop Application (macOS / Windows)

iOS Application (iPhone / iPad)

Apple TV Application (tvOS)

Platform Comparison Matrix

What Will I Hear Differently?

If you are used to hearing content in surround and are now listening through a stereo fold down (on Playback for Web, iOS, or Apple TV), here is what changes perceptually:

In short: You will hear all the important content (dialogue, music, and effects) clearly. The main difference is that surround envelopment is reduced to a front-facing stereo image, and isolated LFE content is removed.

Production Guidance

What to Expect as a Viewer

• If you are joining a session on Playback for Web, iOS, or Apple TV and the host is streaming in 5.1 or 7.1 surround, you will automatically hear a stereo fold down. No action is required.
• The fold down is a reference-quality stereo preview. All dialogue (Center channel) will be clearly audible, mixed equally into both Left and Right. Surround content will be mixed in at -3 dB.
• The LFE channel is not included in the stereo fold down. If the content has significant bass-only elements in the LFE, those will not be audible in the stereo preview.

What to Expect as a Host / Organizer

• The fold down is automatic and transparent. You do not need to configure it.
• Your Desktop application continues to receive the full multichannel stream. If you select stereo output on the Desktop app, you will hear the same Lo/Ro fold down that remote participants hear.
• The fold down does not alter the source stream. All guests on multichannel-capable endpoints (Desktop app with a surround output device) will receive the full discrete channels.

Recommendations for Critical Listening

• For critical stereo evaluation of multichannel content, perform the fold down in your DAW or NLE before streaming, where you have full control over coefficients, limiter settings, and monitoring levels.
• Use the Desktop app with a calibrated stereo output for the most faithful fold down during a live session.
• Remember that the Playback for Web/iOS/Apple TV fold down goes through an additional encode-decode cycle (Opus compression), which may introduce subtle artifacts compared to a direct PCM fold down.

Known Limitations

Frequently Asked Questions

Q: I'm joining a session from my browser. Will I hear the surround mix?
No. Your browser will receive a stereo version. All content is still audible (dialogue, music, effects) but spatial surround information is reduced to a stereo Left/Right image. This happens automatically and requires no setup.

Q: Why does the mix sound slightly different on my laptop compared to the screening room?
In a screening room with a surround speaker system, you hear discrete channels placed around you (front, sides, rear, subwoofer). On your laptop, all of those channels are folded into two speakers. The center channel (dialogue) is blended into both left and right, surround elements move to the front, and the subwoofer channel is removed. The artistic intent is preserved, but the immersive spatial experience is inherently limited by stereo speakers.

Q: Can I hear the full surround mix on my iPhone or Apple TV?
Not currently. The iOS and Apple TV apps receive a pre-mixed stereo stream. To monitor the full discrete multichannel mix, use the Desktop application with a connected surround audio output device (for example, an audio interface routed to a 5.1 or 7.1 speaker system).

Q: Will I miss any dialogue or important audio?
No. Dialogue is typically carried on the Center channel, which is mixed into both Left and Right at nearly full volume (-3 dB). Music and effects in the front Left/Right channels pass through at full level. Surround effects are still audible, just repositioned to the front. The only content that is removed is the LFE (subwoofer) channel, which carries deep bass rumbles and is not intended for stereo speakers.

Q: Why is the subwoofer / LFE channel removed?
The LFE channel carries content at +10 dB relative to the main channels and is designed exclusively for subwoofer playback. Mixing it into stereo speakers at full or even reduced level would cause distortion, bass overload, and mask other elements. Removing it is standard industry practice (per ITU-R BS.775) and is how every major streaming platform, broadcast network, and cinema system handles the fold down.

Q: The stereo fold down sounds louder than the surround version. Is that normal?
Yes. When multiple channels are summed into two, the combined signal level increases. This is expected behavior. If the increase is distracting, reduce your output volume. The relative balance between dialogue, music, and effects remains correct.

Q: Can I adjust the fold down settings (for example, make surrounds louder or quieter)?
Not currently. The fold down uses fixed, industry-standard coefficients (Center and Surrounds at -3 dB). This is not adjustable in any Remoto client. For critical work requiring custom fold down settings, we recommend performing the fold down in your DAW or NLE before streaming.

Q: Does the fold down affect the source stream or what other participants hear?
No. The fold down is applied independently to each participant's output. The original multichannel stream is never altered. A guest on the Desktop app with a 5.1 system will hear full surround, while a guest on Playback for Web will hear stereo, simultaneously, in the same session.

Q: I'm connected to a soundbar / HomePod / AirPods. What will I hear?
You will hear stereo. Even if your device supports Dolby Atmos or Spatial Audio, the Remoto stream arrives as stereo on Playback for Web, iOS, and Apple TV. Apple's Spatial Audio (on AirPods Pro/Max) may apply head-tracked spatialization to the stereo signal for a wider feel, but this is an Apple system feature unrelated to Remoto's fold down.

How the Audio Flows: A Simple View

Below is a simplified view of what happens when a host streams a 5.1 surround session and participants join on different devices:

HOST (Desktop App)
Streams 5.1: L | R | C | LFE | Ls | Rs
                │
                ▼
        ┌───────────────┐
        │   MediaMTX    │  (Streaming Server)
        │   Server      │
        └───┬───────┬───┘
            │       │
   Full 5.1 │       │ Stereo fold down
   (6 ch)   │       │ (2 ch)
            │       │
            ▼       ▼
     ┌──────────┐  ┌──────────────────────────────┐
     │ Desktop  │  │ Playback for Web / iOS /      │
     │ App      │  │ Apple TV                      │
     │ Guest    │  │ Receives:                     │
     │          │  │  L_out = L + C×0.7 + Ls×0.7   │
     │ Hears    │  │  R_out = R + C×0.7 + Rs×0.7   │
     │ full 5.1 │  │                               │
     │ surround │  │ Hears stereo                  │
     └──────────┘  └──────────────────────────────┘

• Desktop guests with a surround system hear the full 5.1 mix as the host intended.
• Playback for Web, iOS, and Apple TV guests hear a stereo version where dialogue remains centered, effects remain clear, and surround elements are blended into the front Left/Right.
• The host's original stream is never modified. Each participant receives the version appropriate for their device.

Glossary