dac.headphone_volume seems to have no effect

[todbot]

I'm not hearing any change when adjusting the dac.headphone_volume property.

Below is my variation of tlv320_simpletest.py running on Adafruit CircuitPython 10.0.0-alpha.3 on 2025-05-02; Raspberry Pi Pico with rp2040. The perceived volume coming out of the headphones is constant

import time, math, time
import ulab.numpy as np
import board, busio, audiobusio, audiocore, audiomixer
import adafruit_tlv320 

SAMPLE_RATE = 44100
CHANNEL_COUNT = 1
BUFFER_SIZE = 2048

i2c_sda_pin, i2c_scl_pin = board.GP16, board.GP17
i2s_bck_pin, i2s_lck_pin, i2s_dat_pin = board.GP20, board.GP21, board.GP22

i2c = busio.I2C(scl=i2c_scl_pin, sda=i2c_sda_pin)
audio = audiobusio.I2SOut(bit_clock=i2s_bck_pin, word_select=i2s_lck_pin, data=i2s_dat_pin)
dac = adafruit_tlv320.TLV320DAC3100(i2c)
dac.configure_clocks(sample_rate=SAMPLE_RATE, bit_depth=16)
dac.headphone_output = True
dac.headphone_volume = -35  # dB, does not seem to work? 

mixer = audiomixer.Mixer(sample_rate=SAMPLE_RATE, channel_count=CHANNEL_COUNT, buffer_size=BUFFER_SIZE)
audio.play(mixer)

# generate a sine wave
tone_volume = 0.5
frequency = 440
length = SAMPLE_RATE // frequency
sine_wave = np.array(np.sin(np.linspace(0, 2*np.pi, length, endpoint=False))
                     * tone_volume * 32767, dtype=np.int16)
sine_wave_sample = audiocore.RawSample(sine_wave, sample_rate=SAMPLE_RATE)

mixer.voice[0].play(sine_wave_sample, loop=True)

while True:
    for db in range(-60, 0, 5):
        print("setting headphone db:", db)
        dac.headphone_volume = db
        time.sleep(0.5)

[todbot]

From looking at the values from the Table 6-24 in the datasheet, I think the setter function in headphone_volume should be something like: gain = int(-2*db)

[BlitzCityDIY]

thanks @todbot i will check this out on monday

[BlitzCityDIY]

so i tried a few things, and had the most success if i change the DAC volume value instead of the headphone volume value. i'll update the library to have a function for that and tag you on the PR for testing if that's okay. one thing that is tricky with this DAC is the order of operations for the multiple gain stages

[BlitzCityDIY]

updated examples and readme to use dac_volume instead with #6