Two strong decades of weathering the whims of the music industry have enabled the Indigo Girls to confidently pursue their musical vision without kowtowing to a single trend. Their strength 20 years on remains the same as it ever was: sincere, melodic songwriting, ear-perfect harmonies, and an allegiance to the natural instrumental tones that support the songs without upstaging their homespun origins. Amy Ray’s “Tether” is brought to life with a solid, unflinching organ from longtime sidewoman Carol Isaacs, layers of electric guitar, and a focused vocal effort from Ray and guest Joan Osborne. Emily Saliers’ title track offers up the sweetness that’s become the duo’s forte. Pedal steel and cello color Saliers’ aching “Come On Home.” Ray’s “Heartache for Everyone” throws in a ska beat. “Cordova” speaks of Ray’s socially conscious side with a subtle effective message of lives sacrificed. Together, the two cover far more ground than either does on their own, with no sign of co-dependence but a love for helping the other achieve their vision within the identity they cultivated at their inception.