The purpose of this study is to contribute to the solution of a small but significant problem: how the differences between the two series of stops in different Mongolic, Turkic and Tungusic languages are realised phon-etically, more specifically what are the roles of aspiration (including preaspiration) and voicing in the production of stops. The Altaic languages are spoken over a large area from Eastern Asia and Siberia to the south-eastern part of Europe. We perform an acoustic study of recordings of Halh Mongolian, Shiliin Gol, Horchin, Baarin, Jalaid, Naiman, Oirad (Kalmuck), Oirad (Torguud), Buriad, Uigur, Kazak, Evenki, Xibo and Yakut. We propose the feature [±laryngeal] to be the original contrast for stops in Altaic languages. We find evidence for an east-to-west cline, the easternmost languages relying on aspiration (as in e.g. Chinese), and the westernmost languages relying on voicing (as in many European languages).