Seeing no other replies - I'll jump in here with my limited experience with the LM567 some 18 to 20 years ago ... My expereince, in the use of LM567's to do TouchTone decoding, was that the more you can do to get the tone (or tone range) of interest as the stonger signal - the better, the cleaner, the fewer false outputs the 567 will show. Seeings how you're working to detect a 12 KHz tone (or signal) - why not high-pass (starting at, say, 10 KHz) or bandpass in the 12 KHz area? My solution to TT decoding was to precede each bank of 567's (two tone ranges) with an appropriate low or high pass op-amp filter. The 567's would then actually 'work' whereas before operation could not in any way be guaranteed ... Jim ----- Original Message ----- From: "Pedro Drummond" To: Sent: Thursday, August 02, 2001 6:06 PM Subject: [EE]: Amplify then filter ? Sorry for the missing tag lead. Here it goes again: ----------- Hello, Gods' oracle. One question: I will be using the 567 filter IC to separate 12kHz signals from regular audio. The problem is that the 12kHz has a much lower amplitude. Should I amplify and then insert the full audio mixture to the 567, or will it be able to detect a much lower signal, at the right frequency ? Thanks in advance. Pedro. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.