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Topics - Tranquility Bass

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31
Performance and Measurements / AES17 - THD+N vs Frequency
« on: October 03, 2020, 01:13:46 PM »
Applies to: EUTs with analogue or digital inputs and analogue or digital outputs.

Aim: To measure the THD+N of the EUT against frequency.

Method
A –1dBFS sinusoidal stimulus is applied to the EUT, successively at each octave frequency between
20Hz and half the upper band-edge frequency. The output of the EUT is passed through a standard
notch filter at the frequency of the stimulus, and also through a low-pass filter at the upper band-edge
frequency (or at 20kHz, whichever is the lower). The RMS amplitude of the residual is measured for
each stimulus frequency.

The results are presented graphically, with THD+N (in % relative to the amplitude of the stimulus)
being plotted for each channel against stimulus frequency.

The test is then repeated with a stimulus amplitude of –20dBFS, the results being overlaid on the
original graph.

32
Performance and Measurements / AES17 - Suppression of Imaging Components
« on: September 27, 2020, 01:07:47 AM »
Applies to: EUTs with analogue outputs.

Aim: To measure the total of HF imaging components beyond the audio band which are output from
the EUT's D/A converter, as a result of applied audio-band signals.

Method
The analogue output of the EUT is measured with a –20dBFS sinusoidal stimulus applied, swept from 10Hz to the upper band-edge frequency or 10kHz (whichever is the lower). Components within the audio band are excluded by using the standard high-pass filter. The total RMS amplitude of all the components above the upper band-edge frequency of the EUT is measured for both channels at each frequency, and plotted graphically. The greatest result for each channel,expressed in dBFS, is also presented at the end of the test.

References
http://resources.prismsound.com/tm/dS3_Applications_Manual_A4nc.pdf

33
Performance and Measurements / AES17 - Inter-channel cross-talk
« on: September 27, 2020, 01:00:42 AM »
Applies to: EUTs with analogue or digital inputs and analogue or digital outputs.

Aim: To measure the inter-channel cross-talk between the channels of the EUT at a range of
frequencies.

Method
The input of the EUT's driven channel is fed with a sinusoidal stimulus at –20dBFS which is swept in
octave steps from 10Hz to the upper band-edge frequency. The input to the un-driven channel (if
digital) is fed with a digital-zero signal or (if analogue) is terminated with 50R (or 25R if unbalanced).
At each frequency, the ratio of the RMS amplitude of the output of the un-driven channel (measured
through a 1/3 octave band-pass filter at the stimulus frequency) to the RMS amplitude of the output of
the driven channel is measured, and displayed graphically in dB against frequency. The un-driven
and driven channels are reversed and the test is repeated. The two channels are overlaid on the
same axes so that worst-case cross-talk can be easily seen.

Conclusion

The UP exhibits a maximum cross-talk of 110dB all of the way up to 10kHz and at least 107dB at 20KHz. Below 1kHz the cross-talk is at least 125 dB  !

Compared with DEQX from Stereophile .

Quote
"Channel separation was excellent, at >115dB in both directions below 1kHz, and still 95dB at 20kHz."

we can see that the Ultimate-Preamplifier is indeed superior in terms of channel separation and cross-talk !

References
http://resources.prismsound.com/tm/dS3_Applications_Manual_A4nc.pdf

34
Applies to: EUTs with analogue or digital inputs and analogue or digital outputs.

Aim: To measure power-line (mains) related products in the output noise of the EUT.

Method
If the EUT has a digital input, it is fed with a digital-zero signal; if the EUT has an analogue input it is
terminated with 50R (or 25R if unbalanced). The operator nominates either 50Hz or 60Hz power-line
frequency.
The RMS summation of the signal components in the EUT output at the power-line (mains) frequency
and its second through fifth harmonic is reported for both channels, in dBFS (in the case of an
analogue measurement, this is equivalent to dB below the specified D/A line-up).
Note: only components at the power-line (mains) frequency and its second through
fifth harmonics are included in this test. Artifacts from a high-frequency switching
power supply are classified as spurious components.

References
http://resources.prismsound.com/tm/dS3_Applications_Manual_A4nc.pdf

35
Performance and Measurements / AES17 - SNR
« on: September 25, 2020, 08:49:17 AM »
Applies to: EUTs with analogue or digital inputs and analogue or digital outputs.

Aim: To measure the output noise of the EUT in the presence of signal.

Method
The EUT is fed with a 997Hz sinusoidal stimulus at an amplitude 60dB below its maximum signal
amplitude (–60dBFS).
The output of the EUT is passed through a standard notch filter at the frequency of the stimulus, and
also through the standard weighting filter. The RMS amplitude of the residual is measured for both
channels, in dBFS (in the case of an analogue measurement, this is equivalent to dB below the
specified D/A line-up), and designated as 'dBFS CCIR-RMS'.
See also: Level Search Routines for fault finding with this test.

Conclusion

The DNR for 8 channel differential current mode from the spec sheet for the ES9038PRO is 132 dB-A directly from the DAC output so this measurement is consistent with that measurement if we take into account the additional Noise Figure of both the IV converter and external buffer amplifiers.

References
http://resources.prismsound.com/tm/dS3_Applications_Manual_A4nc.pdf

36
Performance and Measurements / AES17 - Idle Channel Noise Spectrum
« on: September 25, 2020, 08:47:10 AM »
Applies to: EUTs with analogue or digital inputs and analogue or digital outputs.

Aim: To measure the output noise spectrum of the EUT with no signal present.

Method
If the EUT has a digital input, it is fed with a digital-zero signal; if the EUT has an analogue input it is
terminated with 50R (or 25R if unbalanced).
The RMS amplitude of the output noise of the EUT is measured via the standard weighting filter in a
range of 1/3 octave bands between 20Hz and the upper band-edge frequency. The result is graphed
for each channel in dBFS (in the case of an analogue measurement, this is equivalent to dB below
the specified D/A line-up).

References
http://resources.prismsound.com/tm/dS3_Applications_Manual_A4nc.pdf

37
Performance and Measurements / AES17 - Idle Channel Noise
« on: September 25, 2020, 08:45:06 AM »
Applies to: EUTs with analogue or digital inputs and analogue or digital outputs.
Aim: To measure the output noise of the EUT with no signal present.
Method
If the EUT has a digital input, it is fed with a digital-zero signal; if the EUT has an analogue input it is
terminated with 50R (or 25R if unbalanced).
The RMS amplitude of the output noise of the EUT is measured via the standard weighting filter. The
result is reported for both channels, in dBFS (in the case of an analogue measurement, this is
equivalent to dB below the specified D/A line-up), and designated as 'dBFS CCIR-RMS'.

38
Level-dependent logarithmic gain
Applies to: EUTs with analogue or digital inputs and analogue or digital outputs.

Aim: To measure the change in gain of the EUT with signal amplitude, sometimes called 'deviation
from level linearity'.

Method
A 997Hz sinusoidal stimulus is applied at –5dBFS. The output of the EUT is measured after passing
through a 1/3 octave 997Hz band-pass filter. The gain of the EUT is calculated as being the ratio of its
output amplitude to its input amplitude. The narrow-band noise floor of the EUT is also measured
using the same band-pass filter, but with the stimulus muted.
The stimulus is reapplied, and its amplitude is then reduced in 5dB steps, until it is within 5dB of the
measured narrow-band noise floor, noting the output amplitude at each step and calculating the
inferred EUT gain. The results are graphed for each channel, with relativity to the gain measured at –
5dBFS expressed in dB, as a function of the applied amplitude. At the end of the test, a worst-case
gain deviation (in dB) is also reported for each channel.
When the A/D and D/A portions are available separately, this test should be repeated for each section
independently.

Conclusion:
The Ultimate Preamplifier exhibits exception linearity all of the way down to -130dBFS yielding at least 22 bits of resolution !

References
http://resources.prismsound.com/tm/dS3_Applications_Manual_A4nc.pdf

40
Performance and Measurements / Soft Clipping Test
« on: September 24, 2020, 11:24:11 AM »
Introduction

The Ultimate Pre-amplifier features a soft clipping feature which when enabled, clips in much the same way a push-pull tube amplifier does but does so more accurately and consistently since it is implemented in the digital domain.

Measurements


Conclusion

The soft clipping works extremely well and in textbook fashion according to the measurements below. In fact it works so well there are no more distortion artifacts above 3rd order so even the most ardent of tube aficionados would welcome its tube like characteristics which can be turned on or off at will.




41
Performance and Measurements / Tube Emulation Tests
« on: September 14, 2020, 05:46:38 AM »
Introduction

Whilst all of the other tests posted so far are looking for the best possible distortion and noise measurement, in this case we are going in the opposite direction and purposely trying to add distortion in the same way a tube circuit does.

Measurements

In the following tests we operate different tube profiles whilst keeping the grid bias constant. In all of these tests we are mimicking the way a tube Preamplifier behaves which is exposed to a full scale signal all of the way before the volume control which is unlike a Tube Power Amplifier where the distortion increases with increasing volume control !


Conclusion

These are just three examples of what can be achieved with Tube Emulation as the grid bias control and amplifier type allows many different permutations of altering the tube linearity and hence the distortion profiles !! For tube and SET aficionados the pure 2nd harmonic distortion should be music to their ears !!



43
Performance and Measurements / DAC - THD+N vs Amplitude
« on: September 05, 2020, 01:45:02 PM »
Introduction:

The THD+N vs Amplitude measurements are good for testing a devices linearity and noise performance and see whether there is any dependence of noise with signal level. In this test a stimulus in the form of a 1kHz sinewave is fed to the EUT (equipment under test) to see how it responds. In an ideal test what is fed into the EUT should also be present at its output in proportion and without any other frequency components or artifacts present if the EUT is perfectly linear. However in the real world some non linearity is always present and we expect to see some frequency artifacts in the form  harmonics of the original fundamental test frequency. The random uncorrelated noise is also added to this measurement.

We also use this test to show up a flaw in some Esstech Sabre DAC implementations in the form of a hump in THD measurements at a certain band of signal amplitudes.


44
Performance and Measurements / DAC - IMD vs Amplitude Measurements
« on: September 05, 2020, 01:39:16 PM »
Introduction:

The IMD vs Amplitude measurements are good for testing a devices linearity. In this test, usually two or more tones are mixed together and fed to the EUT (equipment under test) to see how it responds. In an ideal test what is fed into the EUT should also be present at its output at the same relative amplitudes and without any other frequency components or artifacts present if the EUT is perfectly linear. However in the real world some non linearity is always present and we expect to see some frequency artifacts in the form of difference or summation of the two frequencies which show up on a frequency spectrum as side bands around the fundamental test frequencies.

We also use this test to show up a flaw in some Esstech Sabre DAC implementations in the form of a hump in IMD measurements at a certain band of signal amplitudes.

Test Methodology

From Amir's excellent website:-

Quote
Intermodulation Distortion

When an ideal linear system is fed two tones, it produces two tones. But when fed to a system with linearity errors, we get modulation frequencies above and below our two tones. This is called intermodulation distortion. There are many dual tone tests. For this, I have picked the SMPTE test which combines a low frequency (60 hz) with a high frequency (7 kHz) in a 4:1 ratio. Here is the explanation from Audio Precision:

The stimulus is a strong low-frequency interfering signal (f1) combined with a weaker high frequency signal of interest (f2). f1 is usually 60 Hz and f2 is usually 7 kHz, at a ratio of f1_f2=4:1. The stimulus signal is the sum of the two sine waves. In a distorting DUT, this stimulus results in an AM (amplitude modulated) waveform, with f2 as the “carrier” and f1 as the modulation.

In analysis, f1 is removed, and the residual is bandpass filtered and then demodulated to reveal the AM modulation products. The rms level of the modulation products is measured and expressed as a ratio to the rms level of f2. The SMPTE IMD measurement includes noise within the passband, and is insensitive to FM (frequency modulation) distortion.​


45
Performance and Measurements / Internal Generator Test
« on: September 05, 2020, 11:35:27 AM »
Introduction:

The Ultimate-Preamplifier has a built in precision digital waveform generator which is useful for doing spot checks and distortion measurements. When generating waveforms such as sinewaves it uses 32bit precision at 192kHz sample rate so one would expect the distortion of this generator to be very low and way below the distortion and noise of anything else in the chain such as the DAC.

Test Methodology:

To verify the performance of the built in generator we need to exclude anything else in the signal path such as the DAC in the preamp and the ADC in the measurement analyzer which will only swamp the measurements with their own distortions. We can do this in the same way we tested the on-board ADC by feeding the resultant digital signals words directly to the dScope III analyzer via the S/PDIF output on the back of the Preamp since the Coax output can handle the native 192kHz resolution of the test generator.

Conclusions:

From the test results below what can we say except to note that any noise and distortion artifacts are way below anything else in the chain and are so low they don't even indicate on the distortion meters ! So indeed the built in test generator can be used as a reference standard waveform generator !!




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