I'm trying to add microcontroller ADC-based monitoring and metering to an audio project of mine, and I'm finding this to be more difficult than I originally imagined. In this application, I need to be able to capture very fast, short transients, so I really need full audio frequency response, and I need 4 separate channels. So far, most of my microcontroller work with ADCs has been way, way too slow to sample 4 channels at >40kHz, so I was hoping to use an envelope follower so that the ADC sampling could be more like 100Hz or so. So, my basic requirements are peak (not avg or RMS) detection of full audio bandwidth, without requiring the ADC and micro to work at those high frequencies. Also, the incoming signal will be up to +/-12.5V (25V p-p,) but the ADC will be on a 3.3V supply, so the signal needs to be scaled down significantly (about 25% of original scale after rectification.)
First I tried designing my own envelope follower from scratch, just for the fun and challenge. I eventually came up with stuff that works, but it was very cumbersome, although I learned about the downside of saturation and related dependencies on slew rate in the process. Anyway, I finally searched the internet for established answers, added the filter stages I needed for response time and sample rate limits, and ended up with two circuits that basically "work." However, these circuits are so much more complex than I expected. Surely I'm doing something wrong.
Can anyone propose a circuit that does the following:
Thanks in advance for any help!
First I tried designing my own envelope follower from scratch, just for the fun and challenge. I eventually came up with stuff that works, but it was very cumbersome, although I learned about the downside of saturation and related dependencies on slew rate in the process. Anyway, I finally searched the internet for established answers, added the filter stages I needed for response time and sample rate limits, and ended up with two circuits that basically "work." However, these circuits are so much more complex than I expected. Surely I'm doing something wrong.
Can anyone propose a circuit that does the following:
- accept 25V p-p (+/-12.5V peak) audio band signal
- full wave rectify it
- follow envelope of peaks
- low pass filter output for slow decay, allowing low ADC sample rates
- scale output envelope to 0-3.3VDC (or a little lower - just have to not clip ADC input)
Thanks in advance for any help!