Spotify works.
But <5ms is on local files.

Choir's sync engine hands raw PCM audio buffers directly to each device's AVAudioEngine and uses AVAudioTime(hostTime:) to schedule playback against the mach clock with full precision. This architecture is mandatory for sample-level start (every device at the same microsecond).

Spotify and Apple Music don't expose raw PCM to apps because of DRM. The stream is decoded inside a closed player, sample-level access is deliberately blocked at the API. This is part of the music industry's licensing terms.

AmpMe uses acoustic matching: the master phone plays Spotify normally, slave phones listen with the microphone and try to align by ear. This bypasses DRM but the cost is heavy.

Typical AmpMe drift is 200-500 milliseconds. The human ear hears anything above 20ms as "echo" or comb filtering. The most common App Store complaint for AmpMe is exactly this: "sync doesn't hold".

Choir's position is clear: we either do it right or we don't do it. No half measures.

For Spotify Premium subscribers, Spotify has its own "Group Session" feature. Multiple devices share a queue. But each device pulls its own stream from Spotify servers; there is no sync guarantee, devices can play seconds apart depending on network.

This is not the problem Choir solves. It's a problem Spotify doesn't want to solve, because the architecture isn't built for it.

The previous plan parked this in v2.2 as "Cast Mode". 90% of mainstream users live on streaming — closing that door felt too restrictive. v1.0 ships Stream Mode. Choir orchestrates Spotify Connect and Apple Music. Multi-phone stays one session, but ~300ms drift (AmpMe-class). The UI shows an aggressive warning when you pick the mode: "Stream Sync ~300ms drift".

So: Choir's "Tight Sync" mode (local file, <5ms) and "Stream Sync" mode (Spotify/Apple Music, ~300ms) are two parallel promises. Same app, clearly labeled, no mixing. You pay Spotify Premium yourself; Choir takes nothing from it.

Three realistic options, hard to soft:

• Use Choir's Stream Mode: v1.0 includes Spotify Connect and Apple Music. Drift ~300ms (AmpMe-class), but 32 phones in one session. Requires Spotify Premium.
• For local files: buy the track from Bandcamp or iTunes as mp3/FLAC. DRM-free → Tight Sync in Choir (<5ms). Direct artist support.
• For studio reference: use Choir's 3 royalty-free demo tracks. The <5ms sync theory showcase.

Same problem, same answer. Apple Music uses DRM too. Even on its own platform, Apple doesn't expose raw PCM access to Apple Music tracks. Lossless / Hi-Res content also flows through the closed pipeline.