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RE: 3.5dB headroom in off the shelf DAC chips?

Posted by Thorsten (M) on January 31, 2017 at 21:18:31

In Reply to: 3.5dB headroom in off the shelf DAC chips? posted by dave789 on January 31, 2017 at 06:03:21:

Hi,

There are no such DAC chips. The maximum available (Wolfson) is 2dB and it is disabled as default and must be explicitly turned on if desired.

There is a good reason for this.

It is not needed with music (test signals are another story).

Using CD at 44.1kHz as example, a signal that would create the mythical inter-sample overs at those magic 3.02dB would have to be equal to at least one halve period of a 11.05kHz sinewave with a level that is 3dB higher than the signal at lower frequencies.

I am unaware of any musical style or work that would create this situation (maybe something atonal by Philip Glass?), including Trash Metal and Electronica.

Also, modern "PPM" (Peak Programme Meter) would normally catch the inter-sample overs if they operate (as they should) in the analogue domain.

I am not saying that "inter-sample overs" are impossible, but they are extremely unlikely in real music recordings.

Now I can think of a situation where lowering the signal by a certain amount may help.

This is in the case of modern pop recordings where there are often deliberatly 100's of clipping events per minute of music, applied in an attempt to go "more loud". In this case the digital filter would "round off" the hard clipping intentionally applied to the original recording.

The problem with this is that a fixed attenuation is not sufficient to be a true restoration. What is needed actually is a much more complex algorithms, like for example the professional "Re-Life"plugin.

But really, after the signal has been clipped it is garbage. One may apply a range of pseudo-remedial means trying to rescue the baby from the bathwater, but its really hopeless TBH...

Even with 16 Bit Audio we have a considerable dynamic range available, enough to record any symphonic work with full dynamic range without requiring gain-riding or dynamic range compression (they are often applied anyway as the full dynamic range challenges most domestic playback systems).

So resorting to digital domain clipping with music having a much lower dynamic range has no excuse whatsoever and should not be supported in any way.

Thor

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to intolerable pain. Really, what more could we need?

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