Very interesting post! Some on this forum do not support single or double blind testing, however I appreciate your efforts. I had a listen to both files driven from my laptop using Sennheiser 58X headphones - not the best chain, but what I had readily available. I used Audacity to playback, which allowed me to quickly switch between the two files. I think you did a great job of level and timing matching. I have to say I heard little to no difference between the files. There were small differences visible in the waveforms, however using Audacity to calculate to overall spectra of the files they were essentially identical. I tried to post them, however couldn't figure out the process for posting images. In any case, well done on an interesting presentation.
A listening test of two power amps
Hello,
It's my first post here. I've been using two power amp setups for my main stereo and I've been curious to see if I can really discern any acoustic difference between the two. One setup involves a bi-wired high-powered stereo power amp and the other uses a pair of identical lower-powered amps with which the speakers, a pair of Tannoy System 12 DMT II monitors, are vertically bi-amped.
I decided to devise a listening test involving a mono acoustic recording made with a valve-condenser mic positioned at my usual listening position. I've used a relatively simple method to ensure that the recordings are level-matched. I've chosen a mono recording method since my goal is, principally, to evaluate the "tone" of the two recordings. I've been inspired to do this test after reading W. A. James' eBook "High end audio on a budget". The aim of the listening test is to try and discern which power amp setup provides the most realistic rendering of acoustic instruments. I thought that a mono recording might help the listener concentrate on the tone. After listening, I think it does. It's less distracting, especially on piano, where stereo or other multi-mic recording setups tend to splay out the notes across the stereo field.
I made two recordings for the test and will place links below so that the audio can be downloaded. I won't at this point give the make and model of the power amps involved, but this is the method used:
Method
1. I created an audio file with white noise at -10dB RMS and put the file on a Logitech Media Server so that I could play it on my stereo using a Raspberry Pi 3 with Audio Injector Pro card and RCA interface (192kHz 24bit DAC).
2. I then put on an LP on a Pro-ject 1.2 and set the volume to my usual listening level on a Quad 34 preamp. Following this, I then played the white noise and used a decibel meter, positioned next to the mic, to measure the level. It measured 67.3 dB.
3. Still playing the noise, I set the record level on a portable Tascam digital recorder arbitrarily to somewhere above -15dB. The microphone used was a large diaphragm valve condenser mic. The Tascam was set to record at 192kHz 24bit.
4. I then recorded the first track of the LP on the Tascam.
5. After that, I wired up the other amp configuration. I played the white noise and adjusted the volume of the preamp such that the decibel meter again measured 67.3dB at the position of the mic. The volume control on the Quad 34 is stepped, so I was lucky it matched!
6. I then recorded the same track on the LP as before, leaving the Tascam record levels unchanged.
7. I tidied the two recordings in Ardour (trimming start and finish only) and exported each as a 192kHz 24bit Flac file. I did not adjust the gain on either recording.
8. I listened to the recordings on the computer with a pair of AKG K501 headphones and Focusrite Scarlett interface.
Results
At first, I could distinguish a marked difference between the two. But now, I'm uncertain of the first qualitative difference that I'd noticed but I have noticed other more subtle differences (for the moment anyway). And that's why I'm here!
It would be wonderful if some people here could listen to the recordings and say which recording produces the most realistic rendering of the three instruments therein, and why. The instruments being piano, drums and string bass.
I've given the two files nondescript names: e.flac and t.flac. If anyone needs a different format or for me to down-sample, please let me know.
Finally, here are the files:
https://escuta.org/webtmp/e.flac
https://escuta.org/webtmp/t.flac
Cheers,
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- 65 posts total
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OP: Yes, use the speaker terminals to create a line-level input, which you feed to your PC's inputs. It's a little dangerous because your amp CAN fry the inputs. 2.83V is ~ 1 Watt if fed to 8 Ohm speakers. For your listening tests, it doesn't matter what reference level you set, as the multimeter will take several hundred volts, but whatever you pick, use the meter to get you to near millivolt accuracy in terms of level matching. If you attempt to record off the speaker terminals though you have to be sure you keep your voltages low, probably 2V or less at all times. |
"It's am interesting quest, certainly do not be deterred from pursuing your methodology. I do find fault with the logic of searching for what sounds most like live instruments, as if there is some absolute. And there lies the fallacy in the premise. If we can agree that all devices color the sound with distortion, I believe that some of us find some distortions consonant with the fabric of the music, or "pleasurable" if you prefer, and others find different distortion spectra to be closer to the sound of real music. What works for you will not work for me. And this is supported by the wide variety of amplification topologies that sell well in the marketplace. Like finding a mate, there are some faults that one can live with and some that one cannot. Thank goodness we dont all find fault in the same things." viridian Thanks for your message. I don't believe its a fallacy that one can be able to distinguish an excellent reproduction from another. It's just that some people are better at it than others. An excellent recording engineer will be somewhere way up on the scale of this ability, especially when they are working closely with musicians to get the sound that the musician wishes (as they should). An excellent musician will also know and even an excellent audiophile that keeps regular contact with live acoustic performance of music. I think it's our ears that get estranged from the absolute sound of instruments because of our distance from them and because we mostly hear instruments played in amplified settings and via reproduction - and in the case of the listener of recorded music near-exclusively, the ears can be corrupted in feedback loop of "taste" - with his or her preferred sound redefining mentally and incrementally what they believe an instrument should sound like. Certainly, every musician has his or her playing technique/embouchure, etc. which affects the sound as does the sound of the instrument itself and the room, but those familiar with the instruments, room acoustics and with the particular player where possible, playing live unamplified, will be able to get closer to an absolute recognition of natural live performance. So when someone above joked asking if I lived above Carnegie Hall, that would really great and would help me as listener a lot. I have to rely more on memory. But if we want to be good listeners, we do need to know what it is that we're listening to. And I'm not saying what amplifier. It's interesting, I sent the links of the two recordings to a nephew who is also a drummer, but has younger ears than mine. He heard the opposite to me in terms of body and fullness but agreed with me when it came to the cymbals, choosing e.flac as more realistic in this sense. I'm still reserving my final decision on which amp I consider more natural until I can write this little program that lets me switch instantly from one recording to another. I'm also really keen to try eric_squires suggestion. "If you attempt to record off the speaker terminals though you have to be sure you keep your voltages low, probably 2V or less at all times." erik_squires Thanks Erik. Yes, I won't use one of my good recorders for this or the laptop input, but I have a cheap Behringer dongle interface that I can risk. Would it matter if I connect the wires at the amplifier end, as long as the speakers are attached? I can keep the wires shorter that way and won't have to shift heavy speakers around. |
- 65 posts total