Internet download/upload speed

That depends on group size and connection method:
peer-to-peer is faster but limited to about 5 to 6 participants (except all of you have at least 4-core processors) and in most cases port forwarding on the router is needed,
server is slower (twice the network delay) more participants are possible (but not too much, that’s what the still developed mass server is for), no port forwarding needed, except if you run a server yourself which would be better than using a distant public server.
DSL works well, optical is a bit quicker in response time but not too much difference. Cable providers are not the best choice and anything mobile or wireless (except perhaps 5G) has a long transmission delay that makes it unusable.

Read Alex 10-SJ-Commandments and also have a look at the user docs.
SJ is constantly developed by Alex, so it might give times where things won’t work as well as before. But usually that doesn’t take long to be corrected and with any software newer versions may need more processing power.

Internet speed usually isn’t the biggest issue for Soundjack, as long as the connection is stable. Latency, jitter, and packet loss matter far more than raw download/upload numbers, so even DSL can work if it’s reliable and everyone uses wired connections instead of Wi-Fi. Upload speed on DSL can sometimes be the bottleneck, but careful router setup and keeping the network uncluttered often helps. I’ve run into similar trade-offs when working with real-time browser projects and online games on https://onga.io/, where responsiveness matters more than bandwidth, and the same principle applies here.