Lies Damn Lies and USB DAC Technical Measurements

Lies Damn Lies and USB DAC Technical Measurements Or how to manipulate measurements for fun and profit Bob Smith - Sound. Smith Labs

Overview • Overture • Reviewers’ comparison walk-through • Windows specific Audio Engine issues

USB DACs JDS Labs ODAC Violectric V 800

Reviewer A

Reviewer B

Which of the above measurements are real?

1. Odac 2. V 800 3. RME ADI-2 pro as DDC 4. Shiit Eitr DDC

Orientation

Odac Measurement WDM

Odac Measurement ASIO

Odac Measurement WDM at -0. 2 d. BFS

V 800 Measurement WDM

V 800 Measurement ASIO

V 800 Measurement WDM at -0. 2 d. BFS

In our hypothetical example: 1. 2. 3. 4. Reviewer A chose to measure odac using ASIO at 0 d. BFS Reviewer A chose to measure V 800 using WDM at 0 d. BFS Reviewer B chose to measure odac using WDM at 0 d. BFS Reviewer B chose to measure V 800 using ASIO at 0 d. BFS Additionally: 1. 2. 3. 4. Reviewer A chose to measure odac using FFT size 32 K, FFT averages 32 Reviewer A chose to measure V 800 using FFT size 8 K, FFT averages 8 Reviewer B chose to measure odac using FFT size 8 K, FFT averages 8 Reviewer B chose to measure V 800 using FFT size 32 K, FFT averages 32

A Fair Comparison

DDC Section Microsoft Windows Specific

Microsoft Windows Audio Architecture

DDC Measurement System Setup

RME ADI-2 Pro 0 d. BFS - WDM

RME ADI-2 Pro 0 d. BFS - ASIO

RME ADI-2 Pro -0. 2 d. BFS - WDM

Eitr 0 d. BFS - WDM

Eitr -0. 2 d. BFS - WDM

RME ADI-2 Pro 0 d. BFS – ASIO down to -250 d. BFS

Eitr 0 d. BFS – WDM – down to -250 d. BFS

Closing Thoughts • Windows driver paths matter. • Levels are important when using non-ASIO paths. • Measurements should have a statement of test conditions so others may repeat and verify. • Look at any measurement graph with a critical eye and skepticism. • Ask yourself if there may be any biasing motivator by the publisher of the data. Don’t assume.

Example Measurement Setup Picture

Example Measurement Setup Documentation The data presented were acquired as follows: 1. Prism. Sound d. Scope III, picoscope 5243 B 2. DAC unbalanced SE RCA and balanced BAL output XLR 3. 100 Kohm load used for measurements 4. 44. 1 KHz sample rate, 24 bit depth most measurements 5. USB input – Audioquest Forest 6. SPDIF input - Tecnec 75 ohm SMPTE 259 M/292 M Digital Broadcast 7. Unbalance RCA cable - Worlds Best Cable Gotham GAC-2 8. Balanced XLR cable - Canare L-4 E 6 S starquad with Neutrik XLR 9. Vaunix Lab Brick USB hub 10: Shielded 14 AWG and 16 AWG power cables DAC Name here Measurements were performed over after a period of xx hrs of DAC power on time.