DACTests

A collection of audio DACs and testbenches, to aid in evaluating their performance and making improvements.

These examples are referenced in the following series of blog posts:

• http://retroramblings.net/?p=1562

• http://retroramblings.net/?p=1570

• http://retroramblings.net/?p=1578

• http://retroramblings.net/?p=1619

• http://retroramblings.net/?p=1686

DACs

• sigma_delta_dac_1storder - the classic 1st order DAC
• sigma_delta_dac_2ndorder - a slightly modified version of https://github.com/hamsternz/second_order_sigma_delta_DAC/blob/master/second_order_dac.v
• sigma_delta_dac_3rdorder - Borrowed from Mark Watson's Atari 800 repo - common/components/hq_dac.v
• hybrid_pwm_sd - The 1st order hybrid PWM / Sigma Delta DAC I wrote for Minimig back in 2012.
• hybrid_2ndorder - A simplistic 2nd order hybrid PWM / Sigma Delta DAC
• hybrid_2ndorder_filtered - As above but with an extra layer of feedback with low-pass filtering.
• hybrid_pwm_sd_2ndorder - a more elaborate 2nd order DAC with input and feedback filtering. More resource-hungry than the previous DAC, and it's not clear that it's any better.
• threshold_dac - Simply quantises the input to 1 or 0 (sounds awful!)
• random_dac - Adds random noise then quantises, to demonstrate that this is enough to reveal the original signal, albeit with extra noise.
• pwm_dac - simplistic pulse width modulation DAC, as a baseline comparison for the various Sigma Delta DACs.

Tests

• sine - Creates a short sine wave at full amplitude.
• fadeout - Creates a sine wave will falling amplitude.
• asymmetric - As above, but simulates imbalance in rising and falling edges of the output driver.
• constant - Creates a low-level constant signal, to aid in checking for idle tones.
• sweep - A slow ramp from a slightly negative to slightly positive signal, to aid in checking for idle tones.
• pcm - Reads a short audio snippet and runs it through a DAC.

Makefile

To run all tests with all DACs, simple type "make". Alternatively, you can supply the DACS and TESTS variables to select which ones to build and run, like so: make DACS=hybrid_2ndorder\ random_dac TESTS=constant\ pcm