I'm unable to see how a straight wire replaces an amplifying amplifier.
A SWBT requires two amplifiers. The DUT amplifier drives a suitable load, and the monitoring amplifier drives the loudspeakers being listened to. Bypass the DUT amplifier using a switch and passive attenuator, and listen blind whether the presence or absence of the DUT amplifier can be detected. The load for the DUT amplifier can be as complex as one likes, and the test signals can be normal speech or music.I'm unable to see how a straight wire replaces an amplifying amplifier.
I agree that these days, the way you propose is accurate and a lot simpler than the physical straight wire bypass I referred to. When I last did a SWBT, digital recording didn't exist, so it had to be done physically. Doing a digital recording removes the practical difficulty of a real load for the amplifier under test whilst at the same time listening on a different loudspeaker.I prefer recording the DUT amp + att. vs. bypass in the loopback of decent DAC+ADC device and A/B them (in ABX or whatever) afterwards, do numerical analysis etc. This way, the choice of monitoring amp + speakers etc doesn't affect the signal at recording time and this generates a higher usability of the data, it literally represents DUT vs. plain wire with great accuracy. DAC+ADC in cable loopback vs original sample stream can and should be checked for transparency first, as the baseline.
I think the shortfall may come in the methodology and stimulus. If carefully selected real-world music were used for test stimulus and the before and after waveforms compared directly real-time as well as spectral FFT, I think we might start to see more differences and better correlation to listening tests.
A SWBT requires two amplifiers. The DUT amplifier drives a suitable load, and the monitoring amplifier drives the loudspeakers being listened to. Bypass the DUT amplifier using a switch and passive attenuator, and listen blind whether the presence or absence of the DUT amplifier can be detected. The load for the DUT amplifier can be as complex as one likes, and the test signals can be normal speech or music.
Sure it can (perceivably that is), give it to someone whose setup costs $1M and tell him this awesome measured device costs $100 and is in a plastic DIY case, 9/10 they will say it sounds like garbage. I posted this elsewhere, but in one of Toole’s talks, he mentions a double-blind speaker test, where one speaker’s sighted ratings were heavily reduced as it was a plastic sub-sat system than was <1/5 the tower speakers it was compared with.if distortion is low, at all frequencies and permitted loads, frequency response flat and noise low, it can't sound bad.
I have never, ever, heard a product that measure well but sounded bad. It does require, however, for the measurements to be comprehensive, but if distortion is low, at all frequencies and permitted loads, frequency response flat and noise low, it can't sound bad.
That doesn't of course mean that somebody might prefer the sound of something that measures worse.
S.
I have.
How does one measure dynamics. What units are they in? If you can't quantify it, you can't compare or replicate any results.I have. I used to search out things at shows that were positively reviewed and measured by JA of Stereophile, like DACs in particular. These were system sounds of course, but the DAC was a big part of that. Mostly dissapointing. Also amps. Searched shows for good sounding amps for many years and finally came up with 2-3 SS amps that I can finally recommend to customers. The only one of these measured by JA was the D'angostino monoblocks. Very spendy.
All of the characterizations you mention are good, but you leave out one of the most important characteristics, dynamics.
How does one measure dynamics. What units are they in? If you can't quantify it, you can't compare or replicate any results.
S
di/dt and dv/dt is dynamics.
That's covered adequately by slew rate. If an amplifier will provide its full output at 20kHz at low distortion into its rated load, what more do you need?di/dt and dv/dt is dynamics. Dynamics is how accurately does the device reproduce a reference transient waveform. Does it make the full peak voltage? Does it slow the risetime? Does it have good dynamic response when the transient is not layered on top of other low-frequency information? What about when it is?
Look at the impulse response for DACs or step response for amplifiers. This is really all we have and it's woefully insufficient to properly characterize these devices.
That's covered adequately by slew rate. If an amplifier will provide its full output at 20kHz at low distortion into its rated load, what more do you need?
S
Slew rate is not enough.
What signal do you feed the amp to measure slew rate?
I suppose most around here know of the folding chair test:
http://matrixhifi.com/ENG_contenedor_ppec.htm
There was a preference for cheap gear.