Question: when did the grateful dead stop using the wall of sound
[{'answer': 'October 1974', 'provenance': [{'wikipedia_id': '9333186', 'title': 'Wall of Sound (Grateful Dead)', 'start_paragraph_id': 15, 'start_character': 149, 'end_paragraph_id': 15, 'end_character': 161, 'bleu_score': 1.0, 'section': 'Section::::Retirement.\n'}]}, {'provenance': [{'wikipedia_id': '9333186', 'title': 'Wall of Sound (Grateful Dead)', 'start_paragraph_id': 15, 'start_character': 0, 'end_paragraph_id': 15, 'end_character': 322, 'bleu_score': 0.963949056609222, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 9700741840204562159}, 'section': 'Section::::Retirement.\n'}]}]