Bike Sound Sharing
Notes and links about sharing a synchronized soundtrack between bicycles carrying speakers on group rides.
I've spent many years trying to solve two missing pieces for large group bicycle rides such as those found in Portland OR and other major bicycling cities. One of them is sound sharing, where all bikes carrying speakers can connect to the same synchronized soundtrack or live DJ. When achieved, this makes a group ride an extraordinary moving body of music, and is ideal for rides themed around bands or genres or otherwise having a planned playlist. It can also be used for announcements and speeches before a ride, and most generally as a crowd-sourced event-scale speaker system.
I've seen and tested doing this every way commonly known and they all hit a few main problems: ease of adoption by receiving users, maximum distance between transmitter and receivers (head to tail of a ride), and latencies (time delays between the transmitter and the sound actually coming out of a bike's speaker). So to start with, all implementations require zero latency between the receiver's output and the sound coming out of a speaker. That means speakers with an aux/line input and no digital signal processing delays. Even using Bluetooth to get to a speaker can add a 20th of a second. Although one would think such small delays might be a wash between speakers 100 feet apart, in live use the echo effect can be unsettling and muddling.
Here's the many solutions I've owned, tested, or researched, in order of how well they solve the problems of distance, latency, and cost/complexity for the receiving users.
Apps: A good app could handle buffering and time synchronization with unlimited range, and they are beginning to appear, but the choices need review. Spotify does, but it doesn't reliably work and riders need a cheaper and less ethically tainted choice.
Apps to be reviewed: CycleSync, ListenTogether
927MHz stage monitor transceivers: Newest solution seen deployed in Portland, reported distance of 100 yards in actual use. Selectable channels, one transmitter to any number of receivers. Can potentially daisy chain to successive channels. Not cheap, sold as a pair, rechargeable. Primary problem is it's mono. But I've seen a ride use these for in motion sound, then switch to SKAA at end for stereo. Transmitter is best on a stalk with additional antenna.
Recommended Parts: Amazon Shopping List
Spotify "Jam" mode: Requires paid Spotify membership by player and all receivers. No latency under ideal conditions, but I have seen receivers experience significant hiccups, delays, and resyncing. Vast existing user base. Uses his phone data for Internet. After beginning play of a playlist, the DJ taps a tiny icon of multiple speakers to get a "Join the Jam" link or QR code to publish or share. Oddly defaults to collaborative mode, so the DJ must then tap additional controls to disable other users' access to volume and navigation.
Spotify: Home, Jam mode instructions
FM radio: A major radio station is an easy source, or a college or Indie station who can put on a ride's soundtrack. But attention must be paid to using analog receivers since modern digital signal processing chip based radios add significant delay. Digital phase locked loop tuning with analog signal chain is a perfect solution but hardcto find. Or use all identical cheap modern receiver modules for matching latencies. Conceivably one can mobile broadcast from a small transmitter (such as those used in churches for the hearing impaired) on an unused frequency, but FCC limits those to no better distance than other solutions. Quality of antenna and putting it on a stalk help both receiver and transmitter. CB and Shortwave may have longer distance but poor audio quality. Technically it may be possible to pursue a license for a mobile station, but fees and legal responsibilities are involved.
Example zero latency receiver: Sangean DT-220A radio (analog but with digital PLL tuning and an aux out jack)
SKAA: Excellent system for many use cases. Stereo, wide frequency range, but only four receivers per transmitter, and distance under 100 feet in real world use. Available as wands, phone dongle, and built into Soundboks, Ryobi and other speakers. Uses 2.4GHz. As with other radio methods, put it on a stalk for best reception.
SKAA Transceivers "Wet Sounds A-Link Plus": user guide, Product Page, SKAA cmd app
PartyCast (unites many speakers) and TWS (pairs left/right): Built into Soundcore and Anker mobile speakers, low latency, fairly short range similar to BT.
Soundcore Glow speakers: user guide, Product Page, Soundcore app, Instructions
PartyBoost / Connect+: Similar to Partycast, built into some JBL speakers, proprietary.
JBL: Instructions
Streaming Server: Like the online listen function on websites for any radio station, allows any browser to be a receiver. I did extensive testing with custom and commercial server software and found it impossible to synchronize. Trying several phones on the same online stream demonstrates this, even if one hits play at the same moment. The Internet is fundamentally asynchronous and doesn't seem to be a well supported protocol for live, time accurate audio. Even the best software promises "latency as low as four seconds!"
Server software: RocketCast, ShoutCast, IceCast
Bluetooth 5.2+: Reportedly has reduced latency, dramatically increased distance, and multicast! But full implementation of these capabilities are rare.
BT: Auracast Intro, 5.3 Transceiver Dongle
Silent disco headphones: Stereo, multi-channel, 915-928MHz, good distance but not extreme. Difficult to find as electronic modules outside of the actual headphones, which are expensive.
Amazon: Example four user system
Monolithic MP3 and everybody hits play at the same time: Entire multi-hour soundtrack in a single file to prevent inter-track pause differences. Possibly using phones or dedicated media player devices. Compromised mainly by human reflex delays, also player startup time.
Wireless instrument transmitter / receiver pair: Usually one-to-one.
Amazon: Example cheap 2.4GHz system
Infrared: Old-school solution, no latencies, can be done in mono with no ICs. Requires line of site or powerful LEDs and scatter lenses plus lots of reflection.
NerdBait: Example Circuit Diagram
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2024.04.16