Could it be that nobody in the realm of smarty-pants indie rock has heard the one about too many chefs spoiling the broth? Consider some of the current stars of the genre: The Arcade Fire’s eight members pack a stage tighter than a Tokyo subway car. Belle and Sebastian’s shifting lineup could run a smallish liberal-arts college (and quite capably, too). And there may be more members of Architecture in Helsinki than notable buildings in the Finnish capital.

There’s certainly something refreshing about all this multiplicity. For one thing, it’s something different. Big rock gangs break up the tedium of all those quintets, quartets, and trios, and—look out!—the occasional daring duo. The notion of a band as a sprawling collective whose members come and go has something charmingly communal about it, and it offers an antidote to the cheap rock cliché of four angry men united against the world.

But there’s not always strength in numbers, as evidenced by new records from two bands well known for their shifting membership rolls. Broken Social Scene and the New Pornographers, both of which happen to be from Canada, also have in common the burden of high expectations: Both are following up almost-but-not-quite-great albums that left them with zealous followings and the potential for much broader appeal.

It’s clear that Broken Social Scene really does consider itself a scene: The Toronto group counts itself as having a ludicrous 17 members. And even if some actually belong full-time to other bands or play only bit parts, on the new Broken Social Scene, the crowdedness shows. It wasn’t always so. Indeed, in its early, more compact days, BSS was sparseness incarnate: Its debut long-player, 2001’s Feel Good Lost, was a mostly instrumental exercise in postrock ambience. A year later, the group leapt forward with You Forgot It in People, which enhanced its blasé, arty vibe with sharper instrumentation, catchy songwriting, and indelible lyrics (“All these people drinking lover’s spit/They sit around and clean their face with it”). People’s best moments found the band’s now-multitudinous members locked into steady, tightly focused grooves that were rockin’ and hypnotic at the same time.

BSS’ self-titled follow-up adds an unwelcome new element to its sound—something jittery and neurotic, a nagging shrillness, a restiveness that suggests the band may never get into a groove again. It hits you right away, in the album-opening “Our Faces Split the Coast in Half,” which features impatient, scattered drumming, horns that come and go, and a repetitive falsetto from frontman Kevin Drew, whose screechy voice—strained harder than it was on most of People—does unrelenting damage to this album. But the biggest problem here is the layers of gratuitous noise, which sound like the product of too many musicians finding things to keep themselves busy.

The same goes for the semiorchestral “Ibi Dreams of Pavement (A Better Day),” which is reminiscent of the Arcade Fire’s near-chaotic rancor but lacks that band’s dash of sweetness. When Drew delivers the tune’s otherwise-catchy refrain—“Well I got shot/Right in the back/And you were there/You were there”—he does it with a distorted shriek that feels like steel wool on the ears. It’s undoubtedly all intended to be a subversion of pop-song convention, but its real effect is to make you notice how ordinary some of these numbers really are. “Windsurfing Nation,” for instance, oscillates wildly while putting no new spin on the neo-postpunk that was all the rage in New York a few years ago, and “7/4 (Shoreline),” sung mostly by BSS breakout Leslie Feist, is tough-chick rock of the kind ready-made for inspirational soundtrack appearances.

Even the smoother and slower songs—the ones rooted in the band’s earlier ambience—now bear an unsettling nail-biting quality. “Major Label Debut,” for instance, is built around a slow and simple acoustic-guitar refrain. But the BSS brigade turns this uncomplicated idea into chaos, piling on the rapid-fire percussion, synth bursts, and stabbing strings. There’s even a recurring human squeal that must have seemed like a great way to give someone something to do in the studio but comes across like a faucet dripping in the middle of the night.

One potential respite is the laid-back “Swimmers,” featuring a welcome vocal appearance by the chilly-voiced Emily Haines of Metric. “If you always get up late, you’ll never be on time,” she sings, not scolding, but with a hushed detachment that fits the song’s New Order–Êisms. Still, like most of this record, it’s not as good as anything on People. Perhaps the only track worthy of that album is the rumbling bass- and toms-driven “Superconnected,” which, despite Drew’s electronically warped vocals, is one of the album’s more streamlined tracks. In other words, it actually sounds like something that could have been made by fewer than 10 people. And it makes you wonder whether this scene might be better off narrowed down to a small clique.