Mono Audio Accessibility Setting Can Clip Audio

Number:rdar://34616660 Date Originated:2017-09-24
Status:Closed Resolved:2017-09-28
Product:Accessibility Product Version:iOS 11.0
Classification:Other Bug Reproducible:Always
When engaging the Mono Audio Accessibility setting in iOS, the Left and Right audio channels are summed, but not divided by 2. This can clip the output of the iOS device.

Steps to Reproduce:
1. Create a mono audio file with a full-scale sine wave output.
2. Play that file on iOS with volume at max -- observe that output is clean.
3. Turn on Mono Audio.

Expected Results:
No change in output -- output should be (L+R)/2, which means no change for a mono source. 

Actual Results:
Output clips. It seems that output increases in level by 6dB because it is not being divided by 2.

iOS 11.0 (15A372)


Well, this is embarrassing -- this bug was present for years, but I just went to verify and submit photographs of the issue with a scope, and it appears to have been fixed in iOS 11! 👏👏👏


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