My current project calls for a Peak Programme Meter - a peak-reading level meter with fast attack, slow decay and a logarithmic scale. My system microcontroller reads the level value periodically from the SigmaDSP (an ADAU1701), compares the value to a set of log-spaced thresholds and drives a row of LEDs.
In theory, the Sigma end of things should be easy - just use the Peak Envelope detector with an appropriate choice of hold and decay times. However, I have fallen foul of the fact that (as was flagged up here: http://ez.analog.com/message/50275#50275) the Envelope detectors have a linear decay characteristic rather than the more usual RC/constant-dB response. The effect of this is that my logarithmic meter decays ridiculously slowly at the top end of the scale and much faster at the bottom.
Two questions therefore spring to mind:
1. In the thread mentioned above, AD indicated that there might be a possibility of constant-dB version of the envelope detectors - is there any chance that these might arrive quickly enough to save me?
2. As that seems unlikely, can anyone suggest an alternative method of building a peak detector with fast attack and slow, constant-dB decay?
Any suggestions would be much appreciated.