Misleading Measurements

[pkane2001]

• If a tree falls in a forest and no one is around to hear it, does it make a sound?
• What is the sound of one hand clapping?
• Is Schrödinger's cat alive or dead if nobody checks? (I know -- this one's a stretch...)
• What does digital audio sound like if it's never converted into analog?

All very good questions, no doubt, but what do they have to do with -10dBV? 🤷‍♂️

[pkane2001]

4 hours ago, lucretius said:

5.4

Input for full-scale amplitude

 

     NOTE The characteristic to be specified is the analog signal voltage required to reach digital clipping under normal device settings.

 

In systems where the output is accessible in the digital domain, the input for full-scale amplitude shall be the r.m.s. voltage of a 997-Hz sine wave that shall be applied to the input to obtain a digital signal whose positive peak value reaches the positive digital full scale.

 

and this:

 

6.3 Output amplitude at full scale

 

In systems where the input is accessible in the digital domain, the output amplitude at full scale shall be the r.m.s. voltage that results from a sine wave whose positive peak value reaches the positive digital full scale under normal settings of gain controls.

**************************************

 

Color me confused.  Perhaps someone can explain to me what is meant in 5.4 and 6.3 above.

 

 

Didn't read the document, but from your quote, it's just saying that analog input/output required to produce a full-scale signal (at input or output) is to be reported as the RMS voltage of a sine wave, rather than its peak value. For example, when 0dBFS is reported to require 2v input, this means 2v RMS, not peak. The actual voltage that produces 0dBFS is then the peak value of about 2.8v.

 

[pkane2001]

1 hour ago, bluesman said:

The entire document and its intent are confusing.  It refers to an analog input driving a digital device, which is already a bizarre and conflicting circumstance for a document that purports to be for the "measurement of digital audio equipment".  And it describes the input signal as "... the maximum analog signal that may be applied to the device for correct operation". 

 

It is clear that the document is referring to devices that have at least an analog input or an analog output, including devices accepting or producing a digital representation of the signal. In other words, analog devices, as well as, devices containing ADCs and/or DACs. 

[pkane2001]

5 hours ago, lucretius said:

 

That's how I read it.  However, if we set 2v RMS* = 0 dB FS, then the peak value is 2.8v only for the 1k sine wave, Music can actually produce a greater peak value than 2.8v, meaning you could have peak values greater than 0 dB on the meter (which of course is measuring the analog peak).

 

*assuming this is max RMS

 

 

As @March Audio said, the RMS value varies with the waveform. Peak value corresponding to 0dBFS is the maximum output.

[pkane2001]

6 minutes ago, lucretius said:

 

Actually. it's peak value corresponding to full scale sine wave.

 

No. 0dBFS applies to all waveforms, it cannot be exceeded.