Measuring the "sound signature" of two different integrated amplifiers.
Extraordinary claims require extraordinary evidence.
I have two high-performance integrated amps. The identities of these amps are not important and both reach "blue region" status for 1 kHz test tones for SINAD at 5 watts/4 ohms. I am presenting these measurements to showcase how
@pkane's Deltawave tools can be used to correlate subjective listening impressions with actual measurements/science. Thank you
@pkane for reviewing my methodology.
1. Background
When comparing two integrated amps at my normal quiet listening levels, I felt as if one system had better "attack" or "PRAT" to the music and I wanted to try to measure it.
My subjective impression is what started this process. I had no measurements beyond sighted bias of having two units with very high 1 kHz tone performance. The TLDR is that I was successful in proving that differences can be measured and it turned out to be some sort of volume compression for transients that would be within the threshold of audibility.
Music on test: Concerto symphonique No. 4 in D minor, Op. 102: Scherzo from SFS0060 -
Masterpieces in Miniature (physical SACD)
System A: SACD player -- balanced--> Integrated Amp 1
"subjective greater attack to the piano notes"
System B: SACD player -- balanced--> Integrated Amp 1 --> tape out --unbalanced--> Integrated Amp 2
System C: SACD player --unbalanced--> Integrated Amp 2.
Recording system:
E1DA Cosmos ADC Grade A with 4.48 ohm Dale Vishay 1% NH-250 resistors, 32-bit/176 kHz
Windows Laptop on battery power for recordings
Classical musical content was used for measuring the sound signature.
2. Matching the Volume
Using System B, I attached real bookshelf speakers (~87 db/2.83V) and set the volume to the actual level I prefer listening to. It's a small room and this was around 68-70 dB at the listening position for the soft portions of the music. Normal piano practice is quoted as 60-70 dB. System B was chosen as the reference volume setting since Integrated Amp 2 has no display indicating the volume, so once it's set, it's set. I then detached the speakers and replaced it with an E1DA Cosmos ADC setup and made a recording of the first minute. I switched to System A with real speakers, set to the same volume by ear, made a recording and then evaluated peaks at various frequencies from Audacity (not just 1 kHz). The volume difference was not linear in Audacity and then based upon my best estimate, I adjusted the volume of System A to get proper volume matching to System B.
System A and System B were matched to 0.056 dB for the SPL peaks in analog (prior to any digital correction).
3. Validation of test environment precision
System A was measured twice, one day apart.
System B was measured twice, one day apart.
System C was measured twice, 3 hours apart.
Deltawave was used to compare the run-to-run variability, trimmed at start and end of the music for the middle ~50 seconds of analysis.
The PK Metric was created by Paul K, the inventor of DeltaWave, and is designed to "more directly answer the question of whether the difference between two devices is likely to be audible or not."
These results show that the test environment (the amplifiers being tested, the cables, the ADC, etc.) were all very precise and are able to generate reproducible results.
PK Metric showed very high precision of the test environment
System A repeated one day later. -120.4 dbFS
System B repeated one day later. -117.2 dbFS
System C repeated 3 hours later. -117.8 dbFS
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4. System A vs. System B
Initial peak values Reference: -28.017dB Comparison: -28.073dB
Initial RMS values Reference: -50.67dB Comparison: -49.022dB
Final peak values Reference: -28.017dB Comparison: -29.707dB
Final RMS values Reference: -50.67dB Comparison: -50.647dB
Recall that I matched volume in analog by making a recording and then using the Peak DB tool for various frequencies in Audacity. That's the initial value. I got my peaks within 0.056 dB of each other yet the RMS values were off by more than 1.5 dB. DeltaWave digitally corrects the level based upon RMS and got the two recordings to <0.03 dB matching. In doing so, the peak values are different by about 1.7 dB.
The differences in volume are non-linear. Sometimes System A (blue) is louder than System B (white) and sometimes it's not. It's not consistent to a single channel either.
View attachment 234845
View attachment 234846
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Subjectively, I liked System A better because it had better "attack." When analyzing the two recordings, we see that
System B actually has a subtle compression effect relative to System A
or
System A was adding artificial impulse relative to System B.
The opposite could be true. System A could be adding artificial volume to impulse. We don't know what is actually more correct. It just shows that there is a measurable difference between these two systems in a manner that makes sense that it could be audible.
The PK Metric is -48.6 dBFS.
5. System A vs. System C
System B has the limitation of running through the tape out of the integrated amplifier in System A. Is the compression effect from the circuitry in the tape out, or from the amplifier? To answer this question, the SACD Player was connected directly to Integrated Amp B. The resulting recording was quieter and so the volume knob on Integrated Amp 2 was raised to attempt to match the volumes. These recordings were a day apart!
Initial peak values Reference: -28.017dB Comparison: -28.571dB
Initial RMS values Reference: -50.605dB Comparison: -49.532dB
Final peak values Reference: -28.017dB Comparison: -29.563dB
Final RMS values Reference: -50.605dB Comparison: -50.443dB
The matching wasn't as good in the analog realm with the peak values differing by around 0.5 dB. However, once Deltawave corrected the RMS values to <0.2 dB deviation, the peaks are still >1.5 dB different.
The tape out circuitry was not responsible for any of the perceived compression effect.
The PK Metric is -48.6 dbFS.
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6. System B vs. System C
The difference between B and C is the tape loop. We have the same integrated amplifier being used in both. Once the two recordings were calibrated by DeltaWave, the RMS was ultra-precise at 0.004 dB and the peaks really aren't different (<0.01 dB). These recordings were a day apart!
Initial peak values Reference: -28.073dB Comparison: -28.571dB
Initial RMS values Reference: -49.02dB Comparison: -49.532dB
Final peak values Reference: -28.073dB Comparison: -28.137dB
Final RMS values Reference: -49.02dB Comparison: -49.024dB
Going straight from the SACD player to an integrated amplifier versus having a tape out in the signal chain had very little difference subjectively or objectively. The PK Metric is -93.0 dbFS.
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7. Conclusions
"Attack" isn't a precise description. "PRAT" (pace, rhythm and timing) isn't a precise description. These are simply words to describe subjective experiences where we like one audio system more than another and cannot articulate the differences with more precise language. What you consider "PRAT," I might consider "attack."
But what we can agree upon are volume differences and how differences in volume that are non-linear can change the sound. I won't be able to convince everyone that I heard these differences between the two amplifiers. I'm sure there are those who will say these measured differences are not audible. All I will say is that I heard a difference which is why I embarked on this test and my original "matching volume by ear" got me to nearly to ~1 dB matching which I attribute to the extensive formal training I've had as a classical pianist.
I won't be able to convince everyone that I ran these tests perfectly or setup each component in the chain to its very best. This is why I have separated these as "systems" rather than naming specific components. Running the E1DA Cosmos without optimized gains should actually make it harder to detect differences between the systems. The E1DA Cosmos does not have an input buffer, and maybe that makes a difference from one system to the other.
I won't be able to convince everyone that my selected music or preferred volume is universal.
I'm not trying to convince you that these differences are the most efficient/meaningful uses of your money. There is clear consensus that speaker placement/furniture placement is the best ban for the buck (free), and when it comes to gear, speaker/subwoofers make the biggest impact to sound.
Anything that can be heard can be measured.
Maybe 30-40 years ago, the test equipment wasn't good enough to capture everything audiophiles thought they could hear. In 2022, hobbyist level ADCs are so good that you should expect/demand claims to be backed by measurements. I very easily can substitute my term "attack" with "PRAT." We have seen time and time again that a lot of audiophile tweaks prove to be useless.
Everything measured cannot be heard.
We're still human.
The PK Error Metric is something I just learned about this week. If someone says they can hear something -300 dB away from reference, that's not really believable. Or better stated to be generous, that difference is not going to be meaningful to you unless you have a genetic mutation allowing you to hear something most humans cannot.
The threshold for audibility of the PK Error metric has been stated as -50 dB and my reported differences met this threshold.
Two high-performance amplifiers seem to have measurable differences in one real-world condition that also meets the threshold for audibility.
Both of these amps are rated into the triple-digit watts into 4 ohms and I was pretty much running ~50 milliwatt to ~5W peaks given that the volume was originally set with an ~87 db/2.83V stereo, 5-6 ohm speaker pair near a wall, 7 ft listening distance, resulting in 68~70 dB RMS with presumably 90-92 dB peaks based upon the analysis of the recordings.
Consider adding Track 1 from Masterpieces in Miniature when testing gear.
It's the kind of classical music that can bring a smile to aficionados of the symphony while still being a piece that can be appreciated by those who rarely listen to classical music. I was very surprised that I thought I heard a difference on this track between two integrated amplifiers and maybe this happens to be a very good test.
Check out Masterpieces in Miniature by San Francisco Symphony on Amazon Music. Stream ad-free or purchase CD's and MP3s now on Amazon.com.
www.amazon.com
@amirm