Recent content by trobbins

I guess there is also the effect of response drop off, both of the soundcard's DAC on outgoing signal, and the ADC on signal coming back in, and also related to the analog circuitry in those two signal paths. The soundcard's chipset seems to have some influence in my EMU0404 in that it changes...

Ok, so your comment below is meaningless, as you aren't using the output of the 2i2. Wrt to 'Correct?', then no. It is likely that most will use the voltage across the load to align the signal level you assign within REW, but you can use the attenuated level (ie. the input level to the 2i2) if...

Please clarify what the 2i2 output channel is doing, as you seem to want to use an independent signal source ( Akitika 1 kHz oscillator) ? The Akitika 1 kHz oscillator and the amplifier are the 'input' to your 2i2, which should be attenuated and then connected to the 2i2. Any 'reference' for...

Were you able to do a frequency measurement sweep from the designated output, looped back to the designated input, and see a flat-line amplitude and phase response, and where that frequency response changed levels as the output signal level was varied using soundcard settings? And similar for...

Have you confirmed basic loopback measurement is ok from your designated output to separately each designated input ? That should confirm that you have assigned the inputs and outputs in REW 'Preferences' control correctly.

Did you then make a measurement with input and output cables/connections connecting to same point (input or output) of a powered amp? That may show up environmental noise pickup due to power loops etc. Then perhaps make an RTA measurement with amp with all connections in place and amp on, but...

There are a few ways to modify the 'noise floor' in RTA. I'd suggest focussing more on ensuring you are seeing valid harmonic levels, and in doing so then appreciating how your view of the 'noise floor' evolves with experience. For starters, its worth doing a loopback to act as a benchmark...

Perhaps you need some more tools to self-diagnose your issues. Do you have an alternative sinewave generator, like a 555 powered from a 9V battery, or a USB music player that can play a sinewave, or a test record or tape or cd that can input to your receiver.

Play with it - turn the signal level up and down. Do you have a meter and can it measure a Vrms level?

Ta muchly - I will continue on a little wiser. Last year I had cross-checked a 10kHz sinewave from a GPSDO aligned signal to show an REW calculation of 10,000.11Hz at either 96kHz or 192kHz sampling for my EMU 0404 at FFT lengths of 1M to 4M. That would have had nominal bin width down to...

I am using REW to set up the 12 oscillators (top octave of notes) for an electronic organ, as well as the four octave divider notes generated from each of the 12 oscillators (ie. a 12 x 5 = 60 note span). Each oscillator is valve-based LC, so may have some noisy variation of frequency, and some...

Perhaps limit the frequency scan range to just around the notch to diagnose. Perhaps turn off dither. You could step though the notch with single frequency steps to confirm as well.

sm52 - perhaps re-read post #10. A somewhat similar analogy is when making a resistance measurement with a multimeter - firstly short the probes to determine the 'zero' reading level, and then measure the unknown resistance.

Incorrect. That hand drawing shows a signal looping from the Focusrite Solo RCA (the soundcard output) to the amp input (device under test) to the 8 ohm dummy load, and then back to the Focusrite line input (the soundcard input).

An REW measurement of say frequency response, or to make a calibration, does inherently include a 'loop' as the signal is generated by the soundcard, then exits the soundcard and is then returned to the soundcard input socket. A loopback test in its simplest form just connects the soundcard's...