EarMen Tradutto Digital-to-Analog Converter Measurements

Link: reviewed by James Hale on SoundStage! Xperience on December 1, 2021

General Information

All measurements taken using an Audio Precision APx555 B Series analyzer.

The EarMen Tradutto was conditioned for 30 minutes at 0dBFS (4.3Vrms out) into 200k ohms before any measurements were taken.

The Tradutto offers four digital-input options: coaxial S/PDIF (RCA), optical S/PDIF (TosLink), USB, and Bluetooth. There are two line-level outputs: balanced 4.4mm TRRS and unbalanced RCA. Comparisons were made between unbalanced and balanced line-level outputs, and aside from the 6dB extra voltage over the balanced connection, there were no appreciable differences observed in terms of THD and noise.

All measurements below, unless otherwise stated, are for the coaxial digital input, and the balanced output. Comparisons were made in terms of THD+N between the coaxial and optical input, and none were found. Between the USB and coaxial input, there was an improvement in THD+N (0dBFS, 24/96), where the USB input measured 0.003%, the coaxial input measured 0.0005%.

Published specifications vs. our primary measurements

The table below summarizes the measurements published by EarMen for the Tradutto compared directly against our own. The published specifications are sourced from Earmen’s website, either directly or from the manual available for download, or a combination thereof. With the exception of frequency response, where the Audio Precision bandwidth is set at its maximum (DC to 1MHz), assume, unless otherwise stated, the coaxial digital input (24/96 1kHz sinewave at 0dBFS), the balanced line-level outputs into 200k ohms, a measurement input bandwidth of 10Hz to 90kHz, and the worst-case measured result between the left and right channels.

Our primary measurements revealed the following using the coaxial input and the balanced line-level output (unless specified, assume a 1kHz sinewave at 0dBFS, 200k ohms loading, 10Hz to 90kHz bandwidth):

Frequency response (16/44.1, 24/96, 24/192)

The chart above shows the Tradutto frequency response as a function of sample rate. The blue/red traces are for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz, the purple/green traces are for a 24/96 dithered digital input signal from 5Hz to 48kHz, and finally orange/pink represents 24/192 from 5Hz to 96kHz. The behavior at low frequencies is the same for the digital input—perfectly flat down to 5Hz. The behavior at high frequencies for all three digital sample rates is as expected, offering sharp filtering around 22k, 46k, and 96kHz (half the respective sample rates). The -3dB point for each sample rate is roughly 21.5, 45 and 92kHz respectively. All three sample rates offer “brick-wall”-type behavior. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue, purple or orange trace) is performing identically to the right channel (red, green or pink trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

Phase response vs. sample rate (16/44.1, 24/96, 24/192)

Above are the phase response plots from 20Hz to 20kHz for the coaxial input, measured at the balanced output. The blue/red traces are for a dithered 16/44.1 input at -20dBFS, the purple/green for 24/96, and the orange/pink for 24/192. The Tradutto does not invert polarity. There’s a worst-case phase shift of around 75 degrees at 20kHz for the 16/44.1 signal, 25 degrees for the 24/96 signal, and roughly 10 degrees for the 24/192 input data.

Digital linearity (16/44.1 and 24/96 data)

The chart above shows the results of a linearity test for the coaxial digital input (the optical input performed identically) for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the balanced line-level output. The digital input is swept with a dithered 1kHz input signal from -120dBFS to 0dBFS, and the output is analyzed by the APx555. The ideal response is a straight flat line at 0dB (i.e., the amplitude of the digital input perfectly matches the amplitude of the measured analog output). The 24/96 exhibited perfect linearity down to -120dBFS, while the 16/44.1 data was perfect down to -100dBFS, and only +3dB (left) and +1dB (right) at -120dBFS. Because of this DAC’s exceptional linearity performance, a second measurement . . .

. . . was performed, extending down to -140dBFS. The chart above shows linearity performance down to -140dBFS, where the 24/96 remained within 1dB of flat, which is a phenomenal result. The 16/44.1 data results are as expected, showing significant deviations below -120dBFS. But it is worth highlighting that a linearity result that is flat down to -100dBFS for 16-bit input data is also exceptional.

Impulse response

The graph above shows the impulse response for the Tradutto, for a looped 24/44.1 test file that moves from digital silence to full 0dBFS (all “1”s) for one sample period then back to digital silence. We can see that reconstruction filter employed by EarMen is that of a typical sinc function.

J-Test (coaxial input)

The chart above shows the results of the J-Test test for the coaxial digital input (the optical input performed identically) measured at the balanced line-level output. J-Test was developed by Julian Dunn the 1990s. It is a test signal—specifically, a -3dBFS undithered 12kHz square wave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (i.e., 36kHz) of the 12kHz square wave is removed by the bandwidth limitation of the sampling rate, we are left with a 12kHz sinewave (the main peak). In addition, an undithered 250Hz square wave at -144dBFS is mixed with the signal. This test file causes the 22 least significant bits to constantly toggle, which produces strong jitter spectral components at the 250Hz rate and its odd harmonics. The test file shows how susceptible the DAC and delivery interface are to jitter, which would manifest as peaks above the noise floor at 500Hz intervals (e.g., 250Hz, 750Hz, 1250Hz, etc.). Note that the alternating peaks are in the test file itself, but at levels of -144dBrA (fundamental at 250Hz) down to -170dBrA for the odd harmonics.  The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to also show how well the DAC rejects jitter.

We can see the primary low-level peak at 250Hz at just below -140dBFS (which is in the test file), some of the subsequent harmonics below -150dBFS, and the worst-case peaks adjacent the main 12kHz peak at a just above -140dBrA. This stellar J-Test FFT is an indication that the Tradutto should not be sensitive to jitter.

J-Test (coaxial input, 100ns of injected jitter)

The chart above shows the results of the J-Test test for the coaxial digital input (the optical input performed identically) measured at the balanced line-level output, with additional 2kHz sinewave jitter using the APx555’s built-in jitter generator. While the Tradutto did not manifest perfect jitter immunity, the characteristic sidebands at 10kHz and 12kHz are at a very low -135dBrA down, or 0.00002%. Even with a very significant 1000us of injected jitter (not shown), not only did the Tradutto not lose sync with the signal, but exhibited 10/12kHz sideband amplitudes of only -115dBrA, or 0.0002%. These are outstanding results.

Wideband FFT spectrum of white noise and 19.1kHz sinewave tone

The chart above shows a fast Fourier transform (FFT) of the balanced-line level output with white noise at -4dBFS (blue/red), and a 19.1kHz sinewave at 0dBFS, both fed to the coaxial digital input, sampled at 16/44.1 (purple/green). The sharp roll-off above 20kHz in the white-noise spectrum shows the implementation of the brick-wall-type reconstruction filter. There are no imaged aliasing artifacts in the audioband above the -135dBrA noise floor. The primary aliasing signal at 25kHz is at -110dBrA, or 0.0003%, while the second, third, and fourth distortion harmonics (38.2, 57.3, 76.4kHz) of the 19.1kHz range from -100 to -130dBrA, or 0.001% to 0.00003%.

THD ratio (unweighted) vs. frequency vs. load (24/96)

The chart above shows THD ratios at the balanced line-level output into 200k ohms (blue/red) and 600 ohms (purple/green) as a function of frequency for a 24/96 dithered 1kHz signal at the coaxial input. The 200k and 600 ohms data are very close to one another up until around 5kHz, hovering between 0.0002% and 0.0005%. The right channel also slightly outperformed the right channel by 2-3dB. Beyond 5kHz, THD values peaked for the 600-load data at only 0.0015% at roughly 15kHz.

THD ratio (unweighted) vs. frequency vs. sample rate (16/44.1 and 24/96)

The chart above shows THD ratios at the balanced line-level output into 200k ohms as a function of frequency for a 16/44.1 (blue/red) and a 24/96 (purple/green) dithered 1kHz signal at the coaxial input. The 24/96 and 16/44.1 data are very close to one another, with the same trend of the right channel slightly outperforming the right channel by 2-3dB. THD values are essentially flat from 20Hz to 20kHz, hovering between 0.0002% and 0.0006% across the audioband.

THD+N ratio (unweighted) vs. frequency vs. sample rate (16/44.1 and 24/96)

The chart above shows THD+N ratios at the balanced line-level output into 200k ohms as a function of frequency for a 16/44.1 (blue/red) and a 24/96 (purple/green) dithered 1kHz signal at the coaxial input. Due to the lower noise floor at 24 bits, the 24/96 outperformed the 16/44.1 data throughout, with a fairly constant THD+N value of 0.0005%, compared to the 16/44.1 data at 0.002%.

THD ratio (unweighted) vs. output (16/44.1 and 24/96) at 1kHz

The chart above shows THD ratios measured at the balanced output as a function of output voltage for the coaxial input into 200k ohms from -90dBFS to 0dBFS at 16/44.1 (blue/red) and 24/96 (purple/green). The 24/96 outperformed the 16/44.1 data at lower input stimuli, with a THD range from around 0.2% at 200 uVrms down to 0.0001% at 1Vrms (right channel), while the 16/44.1 ranged from 5% at 200uVrms down to 0.0005% at 2-4Vrms (left channel).

THD+N ratio (unweighted) vs. output (16/44.1 and 24/96) at 1kHz

The chart above shows THD+N ratios measured at the balanced output as a function of output voltage for the coaxial input into 200k ohms from -90dBFS to 0dBFS at 16/44.1 (blue/red) and 24/96 (purple/green). Due to the lower noise floor at 24 bits, the 24/96 outperformed the 16/44.1 data throughout, with a THD+N range from 5% at 200uVrms down to 0.0005% at 3-4Vrms, while the 16/44.1 varied from 50% at 200uVrms down to 0.002% at the maximum output voltage of 4.3Vrms.

FFT spectrum – 1kHz (digital input, 16/44.1 data at 0dBFS)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the balanced output into 200k ohm for the coaxial digital input, sampled at 16/44.1. The worst-case signal harmonics is at 3kHz at -110dBrA, or 0.0003%. We can also see small power-supply noise peak at 60Hz at -130dBrA, or 0.00003%. When an FFT was collected with a bandwidth of 1MHz (not shown), two distinct peaks at 353.8kHz and 351.8kHz could be seen; these peaks are distinct IMD products of the signal and an 8x oversampling clock (44.1kHz x 8 = 352.8kHz).

FFT spectrum – 1kHz (digital input, 24/96 data at 0dBFS)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the balanced output into 200k ohm for the coaxial digital input, sampled at 24/96. Due to the increased bit depth, the noise floor is much lower compared to the 16/44.1 FFT. The signal harmonics are effectively the same as with the 16/44.1 FFT, with the worst-case peak at 3kHz at -110dBrA, or 0.0003%. The remaining signal harmonics are below -120dBrA, or 0.0001%. We also see power-supply related noise peaks at the fundamental (60Hz) at -130dBrA, or 0.00003%, and at the third harmonic (180Hz) at -140dBrA, or 0.00001%. When an FFT was collected with a bandwidth of 1MHz (not shown), two distinct peaks at 769kHz and 767kHz could be seen; these peaks are distinct IMD products of the signal and an 8x oversampling clock (96kHz x 8 = 768kHz).

FFT spectrum – 1kHz (digital input, 16/44.1 data at -90dBFS)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the balanced output into 200k ohm for the coaxial digital input, sampled at 16/44.1 at -90dBFS. The signal peak has the correct amplitude, and we see no signal harmonics above the noise floor within the audioband.

FFT spectrum – 1kHz (digital input, 24/96 data at -90dBFS)

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the balanced output into 200k ohm for the coaxial digital input, sampled at 24/96 at -90dBFS. The signal peak has the correct amplitude, and we see effectively no signal harmonic peaks within the audioband above the -160dBrA noise floor.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, 16/44.1)

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the balanced output into 200k ohms for the coaxial input at 16/44.1. The input dBFS values are set at -6.02dBFS so that, if summed for a mean frequency of 18.5kHz, would yield 4.3Vrms (0dBrA) at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -120dBRA, or 0.0001% for the left channel, and imperceptible above the noise for the right channel, while the third-order modulation products, at 17kHz and 20kHz are at -120dBrA, or 0.0001%.

Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, 24/96)

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the balanced output into 200k ohms for the coaxial input at 24/96. The input dBFS values are set at -6.02dBFS so that, if summed for a mean frequency of 18.5kHz, would yield 4.3Vrms (0dBrA) at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -120dBRA (left), or 0.0001%, and -135dBrA (right), or 0.00002%, while the third-order modulation products, at 17kHz and 20kHz are at -120dBrA, or 0.0001%. This is a stellar IMD result.

Diego Estan
Electronics Measurement Specialist