Here are some great, current, ear training resource guides that are perfect for bass players that want to be able to hear chord progressions better, and pick up melodies faster! this article on reddit has a good extensive list: The Ear Training Resource Guide (http://www.reddit.com/r/musictheory/comments/1mde7c/the_ear_training_resource_guide/) the ear training resources on this list are current with good detail on pros and cons for each! i would also add to that resource list: The Ear Training Guide - Essential Ear Training Exercises (http://www.eartrainanywhere.com/store/products/ear-training-guide-essential-ear-training-exercises/) this ear training resource includes good real-life musical scenarios where each type of ear training practice will help you most! i like this one a lot, because if you find yourself struggling with a certain type of musical scenario, then you will know exactly what type of ear training you need to practice, in order to improve! and also Armen Donelain's Training The Ear Volumes 1 & 2 (http://www.armenjazz.com/bio-biblio.html), this one's particularly good for developing your jazz ear. these volumes are really challenging, but i like that they are very comprehensive! for jazz bass players, i would also like to mention Top Speed and in All Keys: Charlie Banacos's Pedagogy of Jazz Improvisation (http://www.charliebanacos.com/info.html)... So many top jazz musicians studied from this guy and this book will rock your ears! this ear training resource provides other unique ear training approaches that a lot of jazz musicians have adopted into their practice.