measurement standards: noise level / dynamic range / signal to noise ratio

Where can I find measurement specifications, does anyone know links to current documentation?
For example, is it possible to measure the noise level of a sound card with a gain ratio of 1 to 1? (assume the input is ideal and measure only the output)
How is dynamic range measured? i.e. 32 bit integer pcm dr=192 dB , but OVP can add analog clipping at lower amplitude, then i can find max volume without clipping and dr=max vol - noice level and signal to noise ratio = max volume/noice level ?

1. Where to find documentation?​

• Audio Precision Knowledge Base: They are the industry standard for hardware testing. Look for their "Audio Measurement Guide."
• AES17 Standard: The official document for digital audio equipment measurements.
• Archimago’s Musings: A highly respected blog for real-world measurements and methodology.

2. Measuring noise floor at 1:1 (Unity Gain)​

Yes, it is possible and actually standard practice.

• If you assume a "perfect input" (sending a 0 dBFS digital signal or a "digital zero" signal), you are measuring the DAC's idle noise floor.
• In a loopback test (Output → Input), you measure the combined noise of the DAC and ADC. To isolate the output, you would need an external analyzer (like an APx555) that has a noise floor significantly lower than the sound card you are testing.
• 1:1 ratio (Unity Gain) is the best way to compare gear, as it avoids adding gain-stage noise from the pre-amp.

3. Dynamic Range (DR) vs. SNR​

You are touching on the difference between theoretical digital limits and physical analog reality.

• The 32-bit Fallacy: While 32-bit PCM has a theoretical range of 192.6 dB, no physical analog component can achieve this. The best modern DAC chips (like ESS Sabre or AKM) have a physical limit around 130–135 dB due to thermal (Johnson) noise.
• Dynamic Range Measurement: According to AES17, DR is measured by playing a -60 dBFS tone. The device's THD+N is measured, and the "distance" from the peak (0 dBFS) to that noise floor is calculated. This is done at -60 dBFS to ensure the DAC's converters stay "active" (preventing some chips from simply muting the output and "cheating" on noise specs).
• SNR (Signal-to-Noise Ratio): This is the ratio between the maximum undistorted signal (just before clipping) and the noise floor when no signal is present.
• Your Formula: Your logic is correct:

Note on Clipping: If OVP (Over Voltage Protection) or analog stages cause clipping at a lower amplitude than the digital maximum, that "clipping point" becomes your effective 0 dB reference for all calculations. Anything above that is "non-usable" range.