The reason is block size in quality test is too small. It only use 0.0015 ms. When we use 48000 rate, number of samples in one wave is more than 100 for 440 Hz stream. But there are only 72 samples in 0.0015 ms. We have two solutions to fix it.

1. Use 1330 Hz stream for testing.
2. Increase block size.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/9e6bb65583bf0646e33df70425beb4ff1d3c4708

commit 9e6bb65583bf0646e33df70425beb4ff1d3c4708
Author: Yu-Hsuan Hsu <yuhsuan@google.com>
Date: Tue Oct 23 20:01:52 2018

[autotest] audio_AudioBasicExternalMicrophone: Change test frequency

We use 0.0015 ms as block size when checking quality. When the rate is
48000, it is equal to 48000 * 0.0015 = 72 frames. However, the length of
one wave in 440 HZ stream is 48000 / 440 = 109 frames. It is too large to
test. So we change the higher frequency file, 48000 / 1330 = 36 frames is
enough.

BUG=chromium:896141
TEST=run audio_AudioBasicExternalMicrophone.quality test.

Change-Id: I451ab0a992b80d57bfa015576c26ca88f4b000ce
Reviewed-on: https://chromium-review.googlesource.com/1292695
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Yu-Hsuan Hsu <yuhsuan@chromium.org>
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>

[modify] https://crrev.com/9e6bb65583bf0646e33df70425beb4ff1d3c4708/server/site_tests/audio_AudioBasicExternalMicrophone/audio_AudioBasicExternalMicrophone.py

Request merge to M71. It is the fix for audio autotest. It won't break anything. Thanks.

Hello @kalin, I am curious why we only schedule this test suite(chameleon_audio_nightly) on tot-1 but not tot. Thanks.

Approving merge to M71 Chrome OS.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/b01de89c25b27971eaa6c138621f82da8080958c

commit b01de89c25b27971eaa6c138621f82da8080958c
Author: Yu-Hsuan Hsu <yuhsuan@google.com>
Date: Thu Oct 25 02:13:29 2018

[autotest] audio_AudioBasicExternalMicrophone: Change test frequency

We use 0.0015 ms as block size when checking quality. When the rate is
48000, it is equal to 48000 * 0.0015 = 72 frames. However, the length of
one wave in 440 HZ stream is 48000 / 440 = 109 frames. It is too large to
test. So we change the higher frequency file, 48000 / 1330 = 36 frames is
enough.

BUG=chromium:896141
TEST=run audio_AudioBasicExternalMicrophone.quality test.

Change-Id: I451ab0a992b80d57bfa015576c26ca88f4b000ce
Previous-Reviewed-on: https://chromium-review.googlesource.com/1292695
(cherry picked from commit 625e9f8613c8dd1249915e614af02aa4374c8f24)
Reviewed-on: https://chromium-review.googlesource.com/c/1297876
Reviewed-by: Yu-Hsuan Hsu <yuhsuan@chromium.org>
Commit-Queue: Yu-Hsuan Hsu <yuhsuan@chromium.org>
Tested-by: Yu-Hsuan Hsu <yuhsuan@chromium.org>

[modify] https://crrev.com/b01de89c25b27971eaa6c138621f82da8080958c/server/site_tests/audio_AudioBasicExternalMicrophone/audio_AudioBasicExternalMicrophone.py

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