wav sample_rate appears limited to less than 65536

[kevinjwalters]

I wanted to experiment with some non-audio sample playback and made some 8bit wavs to check playback. 64000 is ok but this one at 96000Hz plays slowly and inspecting sample_rate shows why:

>>> wave_file = open("Evillaugh.96000.8bit.mono.wav", "rb")
>>> wave = audioio.WaveFile(wave_file)
>>> wave.sample_rate
30464
>>> 30464+65536
96000

That's on 4.0.0-rc1 which happened to be on the CPX I was playing with. Also checked 4.0.1 which has same behaviour.

I had a very quick look and I saw a lot of 32bit values being used by args and variables I'm not sure where the 16bit 65536 limitation is coming from.

I'd also be interested in any bottlenecks I'll encounter as I try faster sample_rate. Will CPX be capable to playing 100000 or 350000 8bit (or 16bit?) samples per sec from a wav file on the built-in flash?

[C47D]

Appears to me it's because sample_rate is an uint16_t in the audioio_wavefile_obj_t type.

circuitpython/shared-module/audioio/WaveFile.h

Lines 34 to 55 in c5a4e19

	typedef struct {
	mp_obj_base_t base;
	uint8_t* buffer;
	uint32_t buffer_length;
	uint8_t* second_buffer;
	uint32_t second_buffer_length;
	uint32_t file_length; // In bytes
	uint16_t data_start; // Where the data values start
	uint8_t bits_per_sample;
	uint16_t buffer_index;
	uint32_t bytes_remaining;
	uint8_t channel_count;
	uint16_t sample_rate;
	uint32_t len;
	pyb_file_obj_t* file;
	uint32_t read_count;
	uint32_t left_read_count;
	uint32_t right_read_count;
	} audioio_wavefile_obj_t;

While the parsed sample_rate of the wave header format is uint32_t:

circuitpython/shared-module/audioio/WaveFile.c

Lines 38 to 46 in c5a4e19

	struct wave_format_chunk {
	uint16_t audio_format;
	uint16_t num_channels;
	uint32_t sample_rate;
	uint32_t byte_rate;
	uint16_t block_align;
	uint16_t bits_per_sample;
	uint16_t extra_params; // Assumed to be zero below.
	};

And i think it gets truncated here:

circuitpython/shared-module/audioio/WaveFile.c

Line 86 in c5a4e19

self->sample_rate = format.sample_rate;

[kevinjwalters]

Thanks @C47D, I tested 4.1.0-beta.0 last night with an 80kHz sample and this now appears to work fine: https://www.youtube.com/watch?v=WME0PRTvCk8

[C47D]

Glad it worked, it does look beautiful, great music too. Is your project documented somewhere i would like to know more about it!

[kevinjwalters]

I'm still debugging and cleaning code up but will let you know when it's out on t'Internet.

[kevinjwalters]

Published last week: Adafruit Learn: Making oscilloscope images with DACs