Hi All
Firstly, REW is fantastic, with so many features, and I've used it very productively for years. However, strange issue....:
I noticed that (what was previously very level) bass in a test system suddenly showed as rolled off below 100Hz, with exactly the same measurement equipment, speaker, amplifier, REW setup and calibration files etc. I have investigated (details below) and found REW is recording a drop even though the actual amp voltage output and SPL are stable, and it is also recording a massive dip in the treble. REW seems to be suddenly applying some massive distortion to the input frequency-SPL response. Can anyone advise why this may have happened? Will upgrading REW help? What have I missed?
Nothing had changed in my equipment and the setup has been stable for years. But for reference, equipment is REW 5.30, “Mini DSB” calibrated USB mic, Startech “ICUSBAudio2D” soundcard line out to an amp with suitable output capacitors. The amp output under 8ohm load, when powered by the soundcard line out has been frequency-level calibrated using the Startech sound card mic in, and that calibration file was used in all measurements (and had been for years).
I checked the output of the soundcard + amp under load with a multimeter (which has a suitable frequency range – could also have used an oscilloscope) using the REW signal generator and the output is relatively stable below 100Hz, just dropping by about 30% as normal (corrected by my REW calibration), not the 10s of dB that REW is showing.
As a sanity check I even used the same soundcard amp, mic, calibration files setup to check my 15” sub bass speaker, and that is also now showing as very rolled off below 100Hz (when it is not).
I checked the voltage using the soundcard microphone input as the input source to REW with a full REW output frequency sweep and REW again shows the input severely rolled off below 100Hz – and also a massive dip at 14KHz – see pic. So this is reproducing the bass rolloff it started showing when the mini DSB mic is used as the REW input.
I even bypassed the Startech soundcard output and used the headphone out from the PC as the REW output for the sweep (probably not brilliantly flat but good for another sanity check), via the usual amp, then into the soundcard input, and this also shows the same signature bass rolloff and massive dip at 14KHz.
So can anyone advise why REW is suddenly applying / showing massive bass and treble input level changes, which all investigations have shown are not there, and how to solve this? Thanks!
Firstly, REW is fantastic, with so many features, and I've used it very productively for years. However, strange issue....:
I noticed that (what was previously very level) bass in a test system suddenly showed as rolled off below 100Hz, with exactly the same measurement equipment, speaker, amplifier, REW setup and calibration files etc. I have investigated (details below) and found REW is recording a drop even though the actual amp voltage output and SPL are stable, and it is also recording a massive dip in the treble. REW seems to be suddenly applying some massive distortion to the input frequency-SPL response. Can anyone advise why this may have happened? Will upgrading REW help? What have I missed?
Nothing had changed in my equipment and the setup has been stable for years. But for reference, equipment is REW 5.30, “Mini DSB” calibrated USB mic, Startech “ICUSBAudio2D” soundcard line out to an amp with suitable output capacitors. The amp output under 8ohm load, when powered by the soundcard line out has been frequency-level calibrated using the Startech sound card mic in, and that calibration file was used in all measurements (and had been for years).
I checked the output of the soundcard + amp under load with a multimeter (which has a suitable frequency range – could also have used an oscilloscope) using the REW signal generator and the output is relatively stable below 100Hz, just dropping by about 30% as normal (corrected by my REW calibration), not the 10s of dB that REW is showing.
As a sanity check I even used the same soundcard amp, mic, calibration files setup to check my 15” sub bass speaker, and that is also now showing as very rolled off below 100Hz (when it is not).
I checked the voltage using the soundcard microphone input as the input source to REW with a full REW output frequency sweep and REW again shows the input severely rolled off below 100Hz – and also a massive dip at 14KHz – see pic. So this is reproducing the bass rolloff it started showing when the mini DSB mic is used as the REW input.
I even bypassed the Startech soundcard output and used the headphone out from the PC as the REW output for the sweep (probably not brilliantly flat but good for another sanity check), via the usual amp, then into the soundcard input, and this also shows the same signature bass rolloff and massive dip at 14KHz.
So can anyone advise why REW is suddenly applying / showing massive bass and treble input level changes, which all investigations have shown are not there, and how to solve this? Thanks!
