• Status Closed
  • Percent Complete
  • Task Type Bugs
  • Category Music playback
  • Assigned To No-one
  • Operating System Sansa Clip+
  • Severity Medium
  • Priority Very Low
  • Reported Version Release 3.14
  • Due in Version Undecided
  • Due Date Undecided
  • Votes 1
  • Private
Attached to Project: Rockbox
Opened by asymcon - 2017-07-15
Last edited by Bilgus - 2019-08-04

FS#13123 - [Clip+/Zip] Pitch inaccuracy in 48kHz mode

Clip+ and Clip Zip suffers from playback speed inaccuracy of 0.7% compared at 48kHz to 44.1kHz - e.g. 1kHz tone is outputted at 1.007kHz.
While not easily noticeable in normal situations (in specific situations it IS quite apparent), A/B or ABX tests are impossible due to this error.

Out of 10 tested devices (6 Clip+ units, 4 Zips), the issue appears on all of them.
Correcting the error by changing playback rate is somewhat acceptable workaround, but as playback rate setting is not persistent, complete fix would be highly desirable.

Steps to reproduce:
1. Upload any generated sine wave of known frequency
2. Set 48kHz mode
3. Start playback with frequency counter/DMM/soundcard connected to the output

Closed by  Bilgus
2019-08-04 19:02
Reason for closing:  Wont Fix

We changed how the clocks were setup a year ago in order to enable frequency/voltage scaling. You could test with 3.13 and see if the old clocks were more accurate at 48khz.

MikeS commented on 2017-07-15 20:11

I tested with test_sampr a long time ago when AMS targets were first coming into the codebase and many of the samplerate clocks were very inaccurate, 48KHz being quite off the mark.

The plugin allows the samplerate to be changed while playing what should be a constant pitch tone no matter the setting.

There’s no option “Frequency” under Playback settings on 3.13

MikeS commented on 2017-07-16 17:17

True. I don’t recall if recording sample rates were fixed up by then either- recording is half clock speed of dac and the menu should only go to 48. Record on device and play back elsewhere if this has recording. Safest bet is to use a compatible test_sampr for what version you’re testing and get results from that. It’s been around since the early days.

Mike, could you please write me step by step what should I do? I’m not that seasoned user of Rockbox :-) I couldn’t find test_sampr plugin in compiled form - it’s not supplied with vanilla 3.13 and only source code is available for download.
Further, I didn’t get the way through recording - should be 48kHz set in recording options? That would mean I’d have to generate the signal externally and record it through microphone.

Values from 3.14:
8k - 974Hz
11.025k - 1000Hz
12k - 997Hz
16k - 997Hz
22.050k - 1000Hz
24k - 991Hz
32k - 997Hz
44.1k - 1000Hz
48k - 1007Hz
64k - 1018Hz
88.2k - 1000Hz
96k - 976Hz


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