The Siri Guru Granth Sahib is a specific collection of shabads (poems) compiled by the 5th Guru, Guru Arjan in 1604, with a few shabads added in by the 10th and last Sikh Guru, Guru Gobind Singh. It begins with the Japji written by Guru Nanak and includes writings by the first five Sikh Gurus and the 9th Guru, Guru Teg Bahadur. Guru Arjan also included several shabads by Muslim and Hindu saints which match the same frequency. The Sikh Gurus continued in a succession for 250 years until 1708 when the 10th Sikh Guru, Guru Gobind Singh passed the Guruship to this sacred collection of writings, and named it the Siri Guru Granth Sahib. The phrase ‘Shabad Guru‘ denotes the form of the Guru being the Word/Sound so is synonymous with the Siri Guru Granth Sahib.
Gurbani means the words or voice of the Guru, so is often referring to the Shabad Guru as well.
Note: some shabads, considered sacred and in Naad, written by the 10th Sikh Guru, Guru Gobind Singh, were not included in the Siri Guru Granth Sahib. Perhaps the Guru felt the compilation was perfect as it was. These writings are part of a ‘Dasam Granth’ (10th Compilation), and include ‘Jaap Sahib‘, which includes ‘Chattr Chakr Vartee‘ and ‘Ajai Alai.’ These are also considered part of Gurbani as they were from the Guru’s words.