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Howto - Distortion Measurements with REW
Howto - Distortion Measurements with REW
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Old 26th June 2019, 03:31 PM   #111
Morde is offline Morde  Finland
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Howto - Distortion Measurements with REW
Thanks X for the excellent how-to!

I had to purchase me a brand new Focusrite Scarlet 2i2 and attached is my loopback measurement result with -3dBFS digital level and 2,08Vrms analog level using balanced in/out connections and REW signal generator.

I think I’m good now to proceed to amp measurements too...
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File Type: png A9DE61C7-075E-4AC4-AB3F-7D6A5AEBB334.png (218.1 KB, 384 views)
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Old 26th June 2019, 05:23 PM   #112
Morde is offline Morde  Finland
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Howto - Distortion Measurements with REW
...and here is the measurement of my Pioneer Super Linear headphone amp @70 ohm load on the left channel and pushing 100mW of power (2,64Vrms). The digital level of the REW signal gen was -3 dB.

The results seem to be reasonable and it is nice to have this kind of sanity check for the build.
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File Type: jpeg 484F33CA-9FE7-4DAF-A07D-00367277AF02.jpeg (260.2 KB, 368 views)
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Old 27th June 2019, 12:02 AM   #113
xrk971 is offline xrk971  United States
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Howto - Distortion Measurements with REW
Nice work Morde! That was quick!

Great to see people posting measurements of their amps. Many of these are first time ever published results.
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Old 28th June 2019, 08:23 PM   #114
delange is offline delange  Belgium
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Okay, so I measured one channel of the PeeCeeBee V4H amplifier. This is with the amplifier running with an output voltage of 2,83 volts into 8 ohms (dummy load). I used REW as the signal generator.
The plot is attached. The author has far better measurements, so maybe I'm doing something wrong?
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File Type: png PeeCeeBee 1w.png (88.4 KB, 313 views)

Last edited by delange; 28th June 2019 at 08:28 PM.
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Old 29th June 2019, 05:35 PM   #115
gtose is offline gtose  United States
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Howto - Distortion Measurements with REW
Default ESI Juli@

X, thanks for the great guide.

Attached are my results for an internal PCI ESI Juli@ loopback. On your recommendation, I built an Akitika 2ppm oscillator. What an easy and simple kit!

My entire setup is:
- Akitika ->
- jan.didden's Linear Audio Autoranger (The L|A Autoranger | Linear Audio NL, Autoranger for soundcards) for attenuation ->
- TRS balanced output ->
- ESI Juli@'s (ESI - Product Archive: Juli@) balanced input

Overall I'm a happy camper and think this will fit my needs just fine. I was using ARTA before, but think I'll now explore REW a bit more.

Greg

Edit: Noise seems a bit high... I'll need to dig into that, maybe because its a noisy desktop PC next to my AC unit?
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File Type: png akitika-esi-julia-loopback.PNG (126.5 KB, 277 views)

Last edited by gtose; 29th June 2019 at 05:38 PM.
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Old 30th June 2019, 03:22 AM   #116
Panelhead is offline Panelhead
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Default Issue with Apple

I have Mojave installed on my Mac Mini. Could not get a signal on loop back.
Played with every setting and did not get it going. Finally went to Focusrite and saw something about allowing “Microphone” to receive signal back.
Went to permissions and there it was. Gave permission, and bang I had a RTA.
Noise was down around -140 dBSF. But even with REW generator at 0 dB, the 1 kHz Pulse is around -128 dB. Dropping output of generator drops the spike at 1 kHz.
I have clicked a lot of buttons in Focusrite control and in REW when Mojave was not accepting the input.
Changed the output to volts and set it at 1 volt. Still just a little spike.
Cannot see where the signal is being attenuated. I am sure it is something simple that I have done.
Anyone more familiar with the system know why a 0 dB signal and a 1 volt level both generate a pulse at 1 kHz that rises 12 dB or so above the noise baseline?
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Old 30th June 2019, 03:32 AM   #117
Ripcord is offline Ripcord  United States
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This is an older Behringer external interface that I've had for a while, FCA202. It's a firewire device.
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File Type: jpg FCA202.jpg (266.2 KB, 199 views)

Last edited by Ripcord; 30th June 2019 at 03:34 AM.
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Old 30th June 2019, 04:31 AM   #118
Panelhead is offline Panelhead
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Join Date: Dec 2002
Location: Houston
Default Issue with Apple

I have Mojave installed on my Mac Mini. Could not get a signal on loop back.
Played with every setting and did not get it going. Finally went to Focusrite and saw something about allowing “Microphone” to receive signal back.
Went to permissions and there it was. Gave permission, and bang I had a RTA.
Noise was down around -140 dBSF. But even with REW generator at 0 dB, the 1 kHz Pulse is around -128 dB. Dropping output of generator drops the spike at 1 kHz.
I have clicked a lot of buttons in Focusrite control and in REW when Mojave was not accepting the input.
Changed the output to volts and set it at 1 volt. Still just a little spike.
Cannot see where the signal is being attenuated. I am sure it is something simple that I have done.
Anyone more familiar with the system know why a 0 dB signal and a 1 volt level both generate a pulse at 1 kHz that rises 12 dB or so above the noise baseline?
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Old 30th June 2019, 01:02 PM   #119
xrk971 is offline xrk971  United States
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Howto - Distortion Measurements with REW
Panel head,
A very low signal like that looks like you are picking up cross talk from other channel. That is, you have input set to ch 1 but generator is on ch 2?
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Old 30th June 2019, 01:12 PM   #120
as_audio is offline as_audio
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This is a very useful thread.

XRK, please edit your first post in a way that it has line break, no running text,
it is a pain for the eyes regardless of screen size otherwise, thank you.
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