Use backticks not vertical bars to denote variables in comments for /modules/audio_processing

Bug: webrtc:12338
Change-Id: I85bff694dd2ead83c939c4d1945eff82e1296001
No-Presubmit: True
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227161
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34690}
diff --git a/modules/audio_processing/audio_buffer.h b/modules/audio_processing/audio_buffer.h
index 3eecf0d..ab0af44 100644
--- a/modules/audio_processing/audio_buffer.h
+++ b/modules/audio_processing/audio_buffer.h
@@ -71,8 +71,8 @@
   // Usage:
   // channels()[channel][sample].
   // Where:
-  // 0 <= channel < |buffer_num_channels_|
-  // 0 <= sample < |buffer_num_frames_|
+  // 0 <= channel < `buffer_num_channels_`
+  // 0 <= sample < `buffer_num_frames_`
   float* const* channels() { return data_->channels(); }
   const float* const* channels_const() const { return data_->channels(); }
 
@@ -80,9 +80,9 @@
   // Usage:
   // split_bands(channel)[band][sample].
   // Where:
-  // 0 <= channel < |buffer_num_channels_|
-  // 0 <= band < |num_bands_|
-  // 0 <= sample < |num_split_frames_|
+  // 0 <= channel < `buffer_num_channels_`
+  // 0 <= band < `num_bands_`
+  // 0 <= sample < `num_split_frames_`
   const float* const* split_bands_const(size_t channel) const {
     return split_data_.get() ? split_data_->bands(channel)
                              : data_->bands(channel);
@@ -96,9 +96,9 @@
   // Usage:
   // split_channels(band)[channel][sample].
   // Where:
-  // 0 <= band < |num_bands_|
-  // 0 <= channel < |buffer_num_channels_|
-  // 0 <= sample < |num_split_frames_|
+  // 0 <= band < `num_bands_`
+  // 0 <= channel < `buffer_num_channels_`
+  // 0 <= sample < `num_split_frames_`
   const float* const* split_channels_const(Band band) const {
     if (split_data_.get()) {
       return split_data_->channels(band);