Stretching partials while keeping fundamentals fixed sounds horrible due to partial collisions

Evidence

The last way to stretch again requires a computer or reprogrammed synthesizer: leave the fundamentals at their traditional frequencies but stretch all the partials. Again the result is horrible, and again, the reason is all the dissonances that have been caused by the widespread near-collisions of partials. — Eric J. Heller, Why You Hear What You Hear- An…, 2414