A boosterpack for Texas Instruments' MSP430 and Stellaris Launchpad platforms.
The frequency response of a linear system -- be it a simple op amp circuit or the complex acoustics of a concert hall -- is easy to talk about but hard to measure. With this boosterpack, I aim to make the measurement process a little easier.
Most often, we'd like to have our results in digital form, so we can plot it, analyze it, and so forth. That means converting between analog and digital domains, while avoiding issues such as frequency aliasing, quantization noise, clipping, and other non-linearities. The 10- to 12-bit ADCs in the MSP430 and Stellaris Launchpads, while fine for most uses, will exhibit most of these problems unless you, the user, take pains to do things right.
That's hard. You'd need to include anti-aliasing filters, avoid clipping events, and keep the signal amplitude high enough to control quantization noise, for starters. You have to do these things on both sides: the ADC side and the DAC side. Oh, wait... the processors included with the Launchpads don't have DACs.
Once past the engineering issues of moving between digital and analog domains, you're still not home free. Consider what happens when you try to measure the frequency response of a loudspeaker. You drive your speaker with a pure tone (sine wave), and use a microphone to record the response. Sweep the frequency of the sine wave over the range of interest, and you're there, right?
Unfortunately, no. The microphone response is mixed in there, too, but most modern microphones are pretty good. You can probably live with the effects of the microphone response. The real problem is the room. Reflections from the walls, floor and ceiling will introduce huge nulls into your perceived loudspeaker characteristic. The room response effectively overwhelms the loudspeaker response in your measurement. But you say you don't have access to an anechoic chamber?