We present an exploratory analysis of F0 ratio, a proposed method to pick up octave jumps in the speech signal. Such jumps, often considered errors, are possibly indicative of the presence of creaky voice. This paper focuses on co-intrinsic voice quality in Seoul Korean fortis stops, building on previous data, and on the Danish contrastive voice quality stød. The results suggest that in Seoul Korean F0 ratio captures a clear jump upwards indicating a modality switch from creaky to modal voice, with a gender difference observed. This suggests that pitch jumps are not necessarily erroneous but may reflect systematic cues to phonological contrasts cued with creak. In Danish, F0 ratio captures a rising intonational contour for non-stød tokens and is able to categorise between stød and non-stød tokens with high accuracy, although this leaves open the question whether F0 ratio captures modality shifts in Danish, or rather a combination of modality shift and pitch contour differences.