Ramp values to and from a default value while active. #1280
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This reduces the popping sound on initial playback of an audio sample. The M4 DAC has a pop on startup that cannot be prevented. It also does not allow readback so current values of the DAC are ignored. Fixes micropython#1090
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Minor stuff.
I have a basic question. When I heard about doing this I thought you were going to doing the ramping when you started and stopped playing a sample, so that no matter what was at the beginning or end of the sample, the output would smoothly rise to match that. I read the issue in more detail and I realize it was not spec'd that way. [copied this to the issue for discussion there]
shared-bindings/audioio/AudioOut.c
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| @@ -43,13 +43,15 @@ | |||
| //| | |||
| //| AudioOut can be used to output an analog audio signal on a given pin. | |||
| //| | |||
| //| .. class:: AudioOut(left_channel, right_channel=None) | |||
| //| .. class:: AudioOut(left_channel, *, right_channel=None, default_value=0x8000) | |||
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I was trying to think of a more descriptive name for this than "default_value". Maybe "silence_value" or "midpoint value"?. @CedarGroveStudios, is there a standard name?
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The term "quiescent value" is frequently used to describe both the bipolar zero value of the sample stream data and the corresponding unipolar-biased value of the DAC. How does that sound to you? @dhalbert
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Sounds good but @tannewt can weight in too.
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quiescent_value works for me. I don't expect people to change it very often. Will update it soon.
* default_value is now quiescent_value * Use step = -step format for sign switch * Add note about analogout_reset being empty
This reduces the popping sound on initial playback of an audio
sample.
The M4 DAC has a pop on startup that cannot be prevented. It also
does not allow readback so current values of the DAC are ignored.
Fixes #1090