(July 2010) (0) After a decade, incremented version to 1.0. (1)
   Implemented "Peak Hold" functionality in meters and reimplemented meters
   for increased efficiency and lower X resource usage. (2) All volumes are
   represented as decibels, including the 0 to -48dB range of the hardware
   peak-meters, the 0 -to- -144dB attenuation for all inputs to the digital
   mixer, the 0 -to- -63dB attenuation of the analog DAC, and the +18 -to-
   -63dB attenuation/amplification of the analog ADC. (3) All gtk "scale"
   widgets have dB legends; the "PageUp" "PageDown" keys allow rapid
   movement between the marked levels. (4) Got rid of myriad compiler
   warnings and other minor fixes across codebase.

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The "Monitor Inputs" and "Monitor PCMs" tabs contain multiple scale widgets
grouped into L/R pairs and an associated peak-level meter. Each scale
widget represents the 24 bit attenuation value of each input to the
ice1712-based soundcard's digital mixer. This mixer is typically used for
zero-latency monitoring of "live" inputs, alongside backing sounds and
effects coming from the eight channels of PCM feeding the digital mixer.
When many inputs are "hot" simultaneously these scale-widgets attenuate the
inputs going into the digital mixer to prevent the output from clipping.
For details see http://nielsmayer.com/envy24control/envy24mixer-architecture.png

(from http://alsa.cybermirror.org/manuals/icensemble/envy24.pdf )

This is what the above manual says about the Envy24's digital mixer:
> 4.5.5 Multi-Track Digital Monitoring
> 
> The Envy24 integrates a 36-bit resolution digital hardware mixer. The
> width of the data path is strictly to ensure that during processing of
> all the channels, under any condition, no resolution is lost. The
> dynamic range of the end user system will be limited by the range of the
> physical output devices used. In order to maintain identical gain to the
> input stream (i.e. 0dB), the resulting 24-bit is not msb-aligned to the
> 36-bit. The overflow bits correspond to the analog distortion due to
> saturation. The user would need to reduce the overall attenuation of the
> inputs to avoid clipping. Insertion of the digital mixer adds only a
> single sample cycle delay with respect to the original data. This
> extremely low latency all digital mixer provides monitoring
> functionality and can replace a traditional external analog input
> mixer. There are 20 independent audio data streams to mix and control
> the volume.

And here's what it says about the Envy24's hardware peak metering:

> Peak data derived from the absolute value of 9 msb.  00h min - FFh max
> volume. Reading the register resets the meter to 00h.