I want to take an 8 ohm, mono, audio signal that could be as high as 3 watts, and input it into a circuit that would allow adjustment of the pitch up or down. Then it needs to output to a speaker with out affecting the power very much. Would a circuit that could do this be very hard to design? Or are there some out there already I can just copy and build?
On a related note can some one tell me where I can find a simple audio filter to filter out any frequency over 900hz and pass anything lower.... I know I can probably find it on google but thought I would ask while I am writing about the other circuit.
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Chris W
KE5GIX
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Pitch shifting is decidedly non-trivial, and doing it well is much harder. This is one of those times when you need to carefully examine what you are trying to accomplish and see if there is some other way. We'd be glad to help with that if you explain what the ultimate goal is.
If the input signal is known to be a pure sine, then you can use an SSB approach. This is still a bit involved if the sine can have a wide frequency range, since it typically requires a 90 degree phase splitter. If there are harmonics in the input, this won't give a harmonic output, however.
Audio pitch shifters are almost always done digitally. Some very sophisticated algorithms are involved, and even still they often have artifacts.
You need to provide more details here as well. Filters have sloping roll-offs, so you have to decide just how steeply you need to cut off above 900 Hz. If you can tolerate only 6 dB/octave, then you can do this with a resistor and capacitor. Beyond that, there are plenty of tradeoffs along with increasing complexity.
Best regards,
Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis
I have a Kenwood TS 440SA Ham radio HF transceiver. In Morse code mode the BFO is set for a frequency of 800 hz. I would prefer a lower frequency. If the signal is strong and you don't need any filtering then you can simply turn on the RIT function and adjust the frequency quite a bit either way. However if the 250hz narrow band CW filter is being used, you are very limited in how much you can adjust the frequency up or down. So that is what I want to do. I don't remember the exact output of the radio to the external speaker, but I am pretty sure it is 2 or 3 watts.
Same radio, but this time on transmit. What it actually transmits is fine, but the in Morse code mode, instead of the 800hz tone it is supposed to sound when you are keying, it sounds 800hz and at least 2 harmonics of 800 hz. I just don't like the way that sounds, so I want to filter out the harmonics enough that I won't notice it. I'm not sure if 6db per octave is enough. Last night right before MusicMatch crashed my computer again, I had found a low pass filter circuit that claimed 24 or 36db/octave, can't remember. It was comprised of 2 op amps and several capacitors and resistors. It didn't give a specific op amp and I know nothing about them, so when I go to mouser.com to order one, I will need something more specific to narrow it down from what I am sure will be thousands of choices. It was set at 1000hz which would probably work fine given it's high drop off rate. Now that I think about it, the transceiver probably sends the harmonics to the transmitter too, but the bandwidth of the TX in CW mode is probably narrow enough to reject the harmonics.
--
Chris W
KE5GIX
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