Timeline for recording low frequeny using sound card
Current License: CC BY-SA 3.0
8 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Jan 12, 2017 at 11:35 | comment | added | Olin Lathrop | "the demodulated signal had a very high frequency". Then you didn't do something right. The theoretical minimum sample rate is twice the highest frequency of the signal, but more is necessary in reality, depending on how tight your filters are. | |
| Jan 12, 2017 at 5:07 | comment | added | Isra | I Also tried FM modulating the input, but the demodulated signal had a very high frequency, does this has anything to do with the sampling rate of the recorder?@OlinLathrop | |
| Jan 10, 2017 at 6:03 | comment | added | Isra | I also tried to do Am Modulation, I editted the post to show the screenshots, I think the sound card causes this to happen | |
| Jan 10, 2017 at 5:07 | comment | added | Isra | yes I re-built the FM timer555 circuit and the results were a bit noisy, and I also noticed that the FM signal has a slight shift to the right. I can't control the frequency deviation for this circuit and I need it's value if I want to use the demodulation function in matlab. Any suggestions to a better option? I found that XR-2206 and ICL8038 are also used but I don't have them at the moment. I wan't to know which one is better before I order. Thanks | |
| Jan 9, 2017 at 11:46 | comment | added | Olin Lathrop | @Isra: Yes, a V-F converter and FM modulator are basically the same in this application, although there are surely better ways to do this than using a 555 timer. | |
| Jan 9, 2017 at 4:38 | comment | added | Isra | Olin, by "drive a V-F converter with maybe 5 kHz center frequency" do you mean like when using timer 555 to do FM modulation? and when we demodulate the 3-7kHz, we set fc to 5kHz right?. I tried AM modulation of the signals, and when recording, I didn't get anything but silence, and even after demodulating using matlab, I got nothing. Maybe I did something wrong, my modulation was correct (from the oscilloscope). Also, the sensor measures both breathing and heartbeat (will be separated later) & the bigger picture is using 4 of those sensors and transferring them through pc mic (1 channel) | |
| Jan 8, 2017 at 18:33 | comment | added | glen_geek | Separating heart & breath to separate L/R channels seems safe and simple. The fundamental frequency component of breath is certainly sub-sonic (requiring a modulator) but can also contain higher frequencies (snoring, whistling, coughing, voicebox etc). Even so, heart + breath channel bandwidths could still be accommodated within 20 kHz mono. | |
| Jan 8, 2017 at 14:33 | history | answered | Olin Lathrop | CC BY-SA 3.0 |