I am collecting data for a project, where I am measuring the room impulse response by playing a sine sweep from a speaker (QSC K8 1KW Active Loudspeaker) and measuring it from the other side of the room using a microphone array. Even though the sine sweep is very clean (bottom image), there appear to be these "ghost sweeps" in the recordings from the microphone.
If I look at the recording in Audacity it is not clipping. I tried using other microphone systems and have concluded that the clipping must be occurring while the sound is playing, or before that in the signal chain. I have tried playing the sound in different ways (from Audacity, from Python) and the clipping is still occurring. So, I have concluded that the clipping must be occurring somewhere in one of these steps:
- When the signal is sent to the audio interface (MOTU 8M)
- When the audio interface is sending the signal to the speaker
- When the speaker is playing the audio.
- Power source to the speaker?
I have tried using a different speaker (an ADAM studio monitor) still with clipping occurring. The signal is being sent to the speaker via
- A TRS to XLR cable
- and XLR to XLR cable. and I have tried replacing cable 2 (I do not have a replacement for cable 1).
I have also tried lowering the volume of the signal sent to the speaker. This alleviates the artifacts, but even at very low volumes there are still some ghost sweeps! I get a bad signal-to-noise at such volumes.
I have read something about "impedance matching" but I don't really understand. I have seen https://engineering.stackexchange.com/questions/16101/audio-frequency-sweep-spectrogram-artifacts-hints but there does not appear to be an answer.