With its outstanding and truly unique debut full-length album, “Transient,” Chaos Echoes made a very strong case earlier this year for album of 2015. However, with its influences drawing as heavily from the experimental realm as from the domain of metal, what is less certain is in which category the award would be given. Unlike your typical death metal band, the lasting imprint that Chaos Echoes leaves on the listener is owed not simply to a linear series of formulaic, prearranged riffs, but instead to a tapestry of interwoven textures, both oppressively heavy and hauntingly subtle, that are primarily born from improvised rehearsal sessions.