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Topic: Frequency and Slew Rate (Read 2579 times) previous topic - next topic
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Frequency and Slew Rate

This is probably academic, but I think that's what we're here for. I've been thinking about the relationship between frequency in an audio file and how that gets turned into voltage, then into motion. A question arose. Could putting audio of a higher-than-required frequency into an amplifier actually degrade performance? My thinking is as follows:

Say you have a 16khz sine wave playing.
You add a 40 khz wave on top.
At some points the 100hz wave will be moving down, but the 40khz wave will be rapidly pulling it up and down.
The amp is now pulling the 100hz wave down from a slightly higher point than it would have if that hgher frequency were not present.
This will require more power and a lower slew rate to maintain audible accuracy. The same principle applies to the speaker.

I'm sure that the difference would be theoretical with any modern equipment, but I'm still trying to figure out the finer points of audio reproduction and understanding if this was true would help.

Thanks!

Re: Frequency and Slew Rate

Reply #1 –
If an amplifier is slew-rate limited (rather than bandwidth-limited), it will start to distort when hit by high levels at high frequencies. This is a rather academic issue that was discussed at length in the seventies under the name TIM (Transient Intermodulation). While it is conceivable that amplifiers exhibit this, it doesn't seem to be an actual problem with real-world audio amplifiers. Still, it wouldn't be a good idea to feed supersonic noise at high levels to an audio amplifier.

Re: Frequency and Slew Rate

Reply #2 –
Thanks, I am going to look that up. as a follow-up question, what does bandwidth mean in the context of an amplifier?

Re: Frequency and Slew Rate

Reply #3 –
Quote from: nintendoeats on
Thanks, I am going to look that up. as a follow-up question, what does bandwidth mean in the context of an amplifier?

Same as with everything else, the range of frequencies the device can usefully pass.

Re: Frequency and Slew Rate

Reply #4 –
Perfect, thanks.