Link: reviewed by Gordon Brockhouse on *SoundStage! Simplifi* on July 1, 2022

**General Information**

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

The Neo S was conditioned for 30 minutes at 0dBFS (4.5Vrms out) into 200k ohms before any measurements were taken.

The Neo S offers four digital inputs: one coaxial S/PDIF (RCA), one optical S/PDIF, one AES/EBU (XLR), and one USB. There are two line-level outputs (balanced XLR and unbalanced RCA) and two headphone outputs (1/8″ TRS unbalanced and 3.4mm TRRS balanced). There are also LAN (over ethernet) and Bluetooth inputs, as well as HDMI and coaxial digital outputs. There is also a digital volume control. Comparisons were made between unbalanced and balanced line-level outputs for a 24/96 0dBFS input, and aside from the 6dB extra voltage over balanced, there were no appreciable differences in THD+N. In terms of input types (USB, coaxial, optical), there were no differences in terms of THD+N at 24/96 resolution.

The Neo S offers three different digital filter settings, accessible through the touchscreen user menu. These are: Fast Rolloff, Slow Rolloff Minimum Phase, and Minimum Phase Corrected.

The Neo S volume control can provide adjustments in 0.5, 1, 2, or 3dB steps. The step value size can be selected in the user menu. The range is -60dB to 0dB. At -60dB, the output is effectively muted; at -59.5dB, the output over the balanced connectors measured 4.8mVrms; and at 0dB, the output from the balanced connectors measured 4.5Vmrs. Using the headphone outputs does not offer any further gain/output voltage. The volume control is implemented in the digital domain, as every step was exactly 0.5dB, and the channel-to-channel deviation was exactly 0.035-0.036dB at every step, throughout the range, as seen in the table below.

Unless otherwise stated, all measurements are with the coaxial digital input, balanced outputs, the Fast Roll-Off filter, and the volume set to 0dB.

**Volume-control accuracy (measured at line-level outputs): left-right channel tracking**

Volume position | Channel deviation |

-59.5dB | 0.036dB |

-45dB | 0.035dB |

-36dB | 0.035dB |

-23dB | 0.035dB |

-8dB | 0.036dB |

0dB | 0.036dB |

**Published specifications vs. our primary measurements**

The table below summarizes the measurements published by Zidoo for the Neo S compared directly against our own. The published specifications are sourced from Zidoo’s website, either directly or from the manual available for download or included in the box, 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 sine wave at 0dBFS), the line-level or headphone outputs into 200k ohms (line-level) and 300/32 ohms (headphone high/low gain), using a measurement input bandwidth of 20Hz to 20kHz, and the worst-case measured result between the left and right channels.

Parameter | Manufacturer | SoundStage! Lab |

XLR output level | 4.1Vrms | 4.5Vrms |

XLR THD+N (1kHz) | -118dB | -109dB |

XLR noise (no signal, A-weighted) | 2uVrms | 3.5uVrms |

XLR signal-to-noise ratio (20Hz-20kHz BW) | 120dB | 121.6dB |

XLR crosstalk (1kHz, 16/44.1) | -120dB | -121.2dB |

XLR dynamic range | 119dB | 122.0dB |

RCA output level | 2.16Vrms | 2.5Vrms |

RCA THD+N (1kHz) | -116dB | -109dB |

RCA noise (no signal, A-weighted) | 2.5uVrms | 3.5uVrms |

RCA signal-to-noise ratio (20Hz-20kHz BW) | 119dB | 117.4dB |

RCA crosstalk (1kHz, 16/44.1) | -130dB | -119.8dB |

RCA dynamic range | 118dB | 118.1dB |

Frequency response (16/44.1) | ±0.25dB (20Hz-20kHz) | ±0.03dB (20Hz-20kHz) |

Headphone (balanced, low-gain) output level | 2.26Vrms | 2.2Vrms |

Headphone (balanced, low-gain) output power (32 ohms) | 310mW | 151.3W |

Headphone (balanced, low-gain) THD+N | -116dB | -105dB |

Headphone (balanced, low-gain) noise | 1.7uVrms | 6uVrms |

Headphone (balanced, low-gain) signal-to-noise ratio | 118dB | 112.2dB |

Headphone (balanced, low-gain) crosstalk (1kHz, 16/44.1) | -128dB | -120dB |

Headphone (balanced, low-gain) dynamic range | 118dB | 112.7dB |

Headphone (balanced, high-gain) output level | 4.1Vrms | 4.3Vrms |

Headphone (balanced, high-gain) output power (300 ohm) | 110mW | 62.1mW |

Headphone (balanced, high-gain) THD+N | -118dB | -104dB |

Headphone (balanced, high-gain) noise | 3.5uVrms | 10uVrms |

Headphone (balanced, high-gain) signal-to-noise ratio | 120dB | 114.6dB |

Headphone (balanced, high-gain) crosstalk (1kHz, 16/44.1) | -130dB | -120dB |

Headphone (balanced, high-gain) dynamic range | 119dB | 114.8dB |

Headphone (unbalanced, low-gain) output level | 1.5Vrms | 1.45Vrms |

Headphone (unbalanced, low-gain) output power (32 ohm) | 138mW | 66mW |

Headphone (unbalanced, low-gain) THD+N | -114dB | -101dB |

Headphone (unbalanced, low-gain) noise | 3.2uVrms | 6uVrms |

Headphone (unbalanced, low-gain) signal-to-noise ratio | 116dB | 104.2dB |

Headphone (unbalanced, low-gain) crosstalk (1kHz, 16/44.1) | -128dB | -98dB |

Headphone (unbalanced, low-gain) dynamic range | 115dB | 105.3dB |

Headphone (unbalanced, high-gain) output level | 2.7Vrms | 2.9Vrms |

Headphone (unbalanced, high-gain) output power (300 ohm) | 47mW | 27.3mW |

Headphone (unbalanced, high-gain) THD+N | -114dB | -99dB |

Headphone (unbalanced, high-gain) noise | 3.5uVrms | 9uVrms |

Headphone (unbalanced, high-gain) signal-to-noise ratio | 118dB | 109.1dB |

Headphone (unbalanced, high-gain) crosstalk (1kHz, 16/44.1) | -132dB | -98dB |

Headphone (unbalanced, high-gain) dynamic range | 118dB | 110.2dB |

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

Parameter | Left channel | Right channel |

Crosstalk, one channel driven (10kHz, 16/44.1) | -118.4dB | -118.4dB |

Crosstalk, one channel driven (10kHz, 24/96) | -118.1dB | -117.9dB |

DC offset | <-2.8mV | <1.4mV |

Dynamic range (A-weighted, 16/44.1) | 96.1dB | 96.1dB |

Dynamic range (unweighted, 16/44.1) | 93.7dB | 93.6dB |

Dynamic range (A-weighted, 24/96) | 124.8dB | 126.0dB |

Dynamic range (unweighted, 24/96) | 116.1dB | 117.4dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1, 16/44.1) | <-103dB | <-103dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 24/96) | <-106dB | <-109dB |

IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1, 16/44.1) | <-91dB | <-91dB |

IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1, 24/96) | <-97dB | <-102dB |

Maximum output voltage (0dBFS) | 4.458Vrms | 4.477Vrms |

Output impedance (XLR) | 177.9 ohms | 178.1 ohms |

Output impedance (RCA) | 51.8 ohms | 51.9 ohms |

Noise level (A-weighted, 16/44.1) | <71uVrms | <71uVrms |

Noise level (unweighted, 16/44.1) | <98uVrms | <98uVrms |

Noise level (A-weighted, 24/96) | <10uVrms | <10uVrms |

Noise level (unweighted, 24/96) | <18uVrms | <18uVrms |

THD ratio (unweighted, 16/44.1) | <0.00045% | <0.00038% |

THD+N ratio (A-weighted, 16/44.1) | <0.0016% | <0.0016% |

THD+N ratio (unweighted, 16/44.1) | <0.0022% | <0.0022% |

THD ratio (unweighted, 24/96) | <0.00025% | <0.00013% |

THD+N ratio (A-weighted, 24/96) | <0.00036% | <0.00028% |

THD+N ratio (unweighted, 24/96) | <0.00046% | <0.00042% |

Our primary measurements revealed the following using the coaxial input and the balanced headphone output (unless specified, assume a 1kHz sine wave at 0dBFS input, 4.5Vrms into 300 ohms, 10Hz to 90kHz bandwidth):

High gain setting

Parameter | Left channel | Right channel |

Maximum Vrms/0dBFS | 4.326Vrms | 4.347Vrms |

Maximum output power into 600 ohms | 31.14mW | 31.44mW |

Maximum output power into 300 ohms | 62.16mW | 62.76mW |

Maximum output power into 32 ohms | 575.6mW | 581.1mW |

Output impedance (balanced) | 0.5 ohm | 0.5 ohm |

Output impedance (unbalanced) | 0.7 ohm | 0.8 ohm |

Noise level (A-weighted, 16/44.1) | <68uVrms | <68uVrms |

Noise level (unweighted, 16/44.1) | <95uVrms | <95uVrms |

Noise level (A-weighted, 24/96) | <11uVrms | <11uVrms |

Noise level (unweighted, 24/96) | <23uVrms | <23uVrms |

Dynamic range (A-weighted, 16/44.1, max volume) | 96.1dB | 95.8dB |

Dynamic range (A-weighted, 24/96, max volume) | 118.4dB | 119.3dB |

THD ratio (unweighted, 16/44.1) | <0.00064% | <0.00054% |

THD+N ratio (A-weighted, 16/44.1) | <0.0017% | <0.0017% |

THD+N ratio (unweighted, 16/44.1) | <0.0023% | <0.0023% |

THD ratio (unweighted, 24/96) | <0.00051% | <0.00041% |

THD+N ratio (A-weighted, 24/96) | <0.00062% | <0.00051% |

THD+N ratio (unweighted, 24/96) | <0.00073% | <0.00065% |

Low gain setting

Parameter | Left channel | Right channel |

Maximum Vrms/0dBFS | 2.215Vrms | 2.223Vrms |

Maximum output power into 600 ohms | 8.16mW | 8.22mW |

Maximum output power into 300 ohms | 16.3mW | 16.4mW |

Maximum output power into 32 ohms | 151.1mW | 152.2mW |

Output impedance (balanced) | 0.5 ohm | 0.5 ohm |

Output impedance (unbalanced) | 0.7 ohm | 0.8 ohm |

Noise level (A-weighted, 16/44.1) | <35uVrms | <35uVrms |

Noise level (unweighted, 16/44.1) | <49uVrms | <49uVrms |

Noise level (A-weighted, 24/96) | <6uVrms | <6uVrms |

Noise level (unweighted, 24/96) | <12uVrms | <11uVrms |

Dynamic range (A-weighted, 16/44.1, max volume) | 96.1dB | 95.9dB |

Dynamic range (A-weighted, 24/96, max volume) | 117.1dB | 119.0dB |

THD ratio (unweighted, 16/44.1) | <0.00043% | <0.00041% |

THD+N ratio (A-weighted, 16/44.1) | <0.0017% | <0.0017% |

THD+N ratio (unweighted, 16/44.1) | <0.0023% | <0.0023% |

THD ratio (unweighted, 24/96) | <0.00023% | <0.00015% |

THD+N ratio (A-weighted, 24/96) | <0.00036% | <0.00031% |

THD+N ratio (unweighted, 24/96) | <0.00058% | <0.00051% |

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

The plot above shows the Neo S 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 all sample rates—perfectly flat down to 5Hz. The behavior at high frequencies for all three digital sample rates is as expected, offering sharp filtering around 22, 48, and 96kHz (half the respective sample rate). The -3dB point for each sample rate is roughly 21, 46.2, and 92.2kHz, respectively. It is also obvious from the plots above that all three sample rates offered “brick-wall”- type behavior with the default Fast Rolloff filter. 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.

**Frequency response (16/44.1, all three filters)**

The plots above show frequency-response for a 16/44.1 input for all three filters (Fast Rolloff, Slow Rolloff Minimum Phase, and Minimum Phase Corrected) into a 200k ohm load for the left channel only. Fast Rolloff is in blue, Slow Rolloff Minimum Phase in purple, and Minimum Phase Corrected is in red. The graph is zoomed in from 1kHz to 22kHz, to highlight the various responses of the filters around the “knee” of the response. At 20kHz, the Fast Rolloff filter is at -0.03dB, the Slow Rolloff Minimum Phase filter is at -5dB, and the Minimum Phase Corrected filter is at -12.3dB.

**Phase response (16/44.1, 24/96, 24/192 with Fast Rolloff filter)**

Above are the phase response plots from 20Hz to 20kHz for the coaxial input, measured at the balanced output, using the Fast Rolloff filter. 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. We can see that the NEO S does not invert polarity, with a worst-case phase shift of just under 160 degrees at 20kHz for the 16/44.1 data, and within +/-20 degrees or so for the 24/96 and 24/192 input data.

**Phase response (16/44.1, all three filters)**

Above are the phase response plots from 20Hz to 20kHz for a 16/44.1 signal at the coaxial input, measured at the balanced output, for all three filters (Fast Rolloff, Slow Rolloff Minimum Phase, and Minimum Phase Corrected) into a 200k ohm load for the left channel only. Fast Rolloff is in blue, Slow Rolloff Minimum Phase in purple and Minimum Phase Corrected in red. We see that both the Slow Rolloff Minimum Phase and Minimum Phase Corrected filters exhibit far less phase shift between 5kHz and 20kHz than the Fast Rolloff filter.

**Digital linearity (16/44.1 and 24/96 to -120dB)**

The graph 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 data is perfectly linear 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, plotted in the chart below.

**Digital linearity (16/44.1 and 24/96 to -140dB)**

This shows the 24/96 data remained within 0.5dB or so of flat to -140dB, 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 (24/44.1, all three filters)**

The graph above shows the impulse responses 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 for all three filters (Fast Rolloff, Slow Rolloff Minimum Phase, and Minimum Phase Corrected) into a 200k ohm load for the left channel only. Fast Rolloff is in blue, Slow Rolloff Minimum Phase in purple, and Minimum Phase Corrected in red. The default Fast Rolloff filter exhibits a typical sinc function, with symmetrical pre- and post-ringing behavior. The Slow Rolloff Minimum Phase filter exhibits no pre-ringing and very little post-ringing, where the Minimum Phase Corrected filter is somewhere in between the other two.

**J-Test (coaxial input)**

The plot above shows the results of the J-Test test for the coaxial digital input measured at the balanced line-level output of the Neo S. 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 sine wave (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.

The coaxial S/PDIF input shows some of the alternating 500Hz peaks in the audio band but at low levels; below -130dBrA. This is an indication that the Neo S should not be sensitive to jitter.

**J-Test (optical input)**

The optical S/PDIF input shows essentially the same result as with the coaxial input above.

**J-Test with 10ns of injected jitter (coaxial input)**

Both the coaxial and optical inputs were also tested for jitter immunity by injecting artificial sine wave jitter at 2kHz on top of the J-Test test file, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection. Above is an FFT with jitter injected at the 10ns level, and peaks can be seen at -125dBrA. This demonstrates that the Neo S DAC’s jitter rejection is not as robust as the J-test result alone would have indicated. Only the coaxial input is shown because the optical input showed basically the same result.

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

Both the coaxial and optical inputs were also tested for jitter immunity by injecting artificial sine wave jitter at 2kHz on top of the J-Test test file, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection. Above is an FFT with jitter injected at the 100ns level, and peaks can be seen at -105dBrA. This demonstrates that the Neo S DAC’s jitter rejection is not as robust as the J-Test result alone would have indicated. Again, the optical input showed pretty much the same result.

**Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (Fast Rolloff filter)**

The plot above shows a fast Fourier transform (FFT) of the Neo S balanced-line level output with white noise at -4dBFS (blue/red) and a 19.1kHz sine wave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1 (purple/green), using the Fast Rolloff filter. The sharp roll-off above 20kHz in the white-noise spectrum shows the implementation of the brick-wall type reconstruction filter. There are absolutely no imaged aliasing artifacts in the audio band above the -135dBrA noise floor. The primary aliasing signal at 25kHz is at -85dBrA, with subsequent harmonics of the 25kHz peak at or below this level.

**Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (Slow Rolloff Minimum Phase filter)**

The plot above shows a fast Fourier transform (FFT) of the Neo S balanced-line level output with white noise at -4dBFS (blue/red) and a 19.1kHz sine wave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1 (purple/green), using the Slow Rolloff Minimum Phase filter. The roll-off above 20kHz in the white-noise spectrum is shallower than what is seen with the filters above and below. There are absolutely no imaged aliasing artifacts in the audio band above the -135dBrA noise floor. The primary aliasing signal at 25kHz is at -35dBrA, with subsequent harmonics of the 25kHz peak at or below this level.

**Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (Minimum Phase Corrected filter)**

The plot above shows a fast Fourier transform (FFT) of the Neo S balanced-line level output with white noise at -4dBFS (blue/red) and a 19.1 kHz sine wave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1 (purple/green), using the Minimum Phase Corrected filter. The FFT is very similar to the one for the Fast Rolloff filter.

**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 nearly identical; however, the right channel, at 0.0002% and below, did outperform the left channel, which was at 0.0003%. In either case, these are extremely low levels of THD. These data also demonstrate that the Neo S’s line-level outputs are robust and can handle lower impedance loads.

**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 data (right channel) consistently outperformed the 16/44.1 data by about 5dB. Still, all THD values are very low, between 0.0005% and 0.00015%.

**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 with 16/44.1 (blue/red) and 24/96 (purple/green) dithered input data. Once again, the 24/96 outperformed the 16/44.1 data, with a THD range from 0.2% to nearly 0.0001% (right channel) at 4.5Vrms, while the 16/44.1 ranged from 5% down to 0.0004% at 4.5Vrms. It’s important to highlight that large discrepancies in THD ratios at lower input levels are due to the inherently lower 24-bit noise floor of the 24/96 data (*i.e.*, when no signal harmonics are measurable in an FFT, a THD value can only be assigned as low as the noise floor permits). The 24/96 data also shows a slight rise in THD between around 100mVrms and 1Vrms.

**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 with 16/44.1 (blue/red) and 24/96 (purple/green) dithered input data. The 24/96 outperformed the 16/44.1 data, with a THD+N range from 3% down to 0.0005%, while the 16/44.1 ranged from 50% down to 0.002% at the maximum output voltage of 4.5Vrms.

**Intermodulation distortion vs generator level (SMPTE, 60Hz:4kHz, 4:1, 16/44.1, 24/96)**

The chart above shows intermodulation distortion (IMD) ratios measured at the balanced output as a function of generator input level for the coaxial input into 200k ohms from -60dBFS to 0dBFS with 16/44.1 (blue/red) and 24/96 (purple/green) dithered input data. Here, the SMPTE IMD method was used, where the primary frequency (F1 = 60Hz) and the secondary frequency (F2 = 7kHz) are mixed at a ratio of 4:1. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. The 24/96 outperformed the 16/44.1 data, with an IMD range from 0.06% down to 0.0005% between -10 and -5dBFS, then up to about 0.001% at 0dBFS, while the 16/44.1 ranged from 2% down to 0.002% at the maximum output voltage of 4.5Vrms at 0dBFS. The 24/96 data exhibited a slight rise in IMD between -30dBrA and -15dBrA.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the balanced output into 200k ohm for the coaxial digital input, sampled at 16/44.1. We see the third signal harmonic (3kHz) at -110/-120dBrA (left/right), or 0.0003/0.0001%. The second and fifth signal harmonics for the left channel are visible at -125dBrA, or 0.00006%, just above the noise floor. There are also no power-supply noise peaks to speak of to the left of the main signal peak.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the balanced output into 200k ohms 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. We see signal harmonics ranging from -110/-120dBrA (left/right), or 0.0003/0.0001% at 3kHz, down to -140dBrA, or 0.00001%. With the lower noise floor, we can see higher even order harmonics, for example at 4 and 6kHz where the peaks are just below -140dBrA, or 0.00001%. Here we see low level peaks on the left side of the main signal peak, at -130dBrA, or 0.00003%, and below.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the balanced output into 200k ohms for the coaxial digital input, sampled at 16/44.1 at -90dBFS. We see the main peak at the correct amplitude, and no signal harmonics above the noise floor within the audio band.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sine-wave stimulus, measured at the balanced output into 200k ohms for the coaxial digital input, sampled at 24/96 at -90dBFS. We see the main peak at the correct amplitude, and power-supply related harmonics at 60Hz, 180Hz, 300Hz, etc., at -130dBrA, or 0.00003%, and below.

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

Shown above is an FFT of the intermodulation (IMD) products for an 18kHz + 19kHz summed sine-wave 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 4.5Vrms (0dBrA) at the output. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) cannot be seen above the -130dBRA, or 0.00003%, noise floor, while the third-order modulation products, at 17kHz and 20kHz, are just above (left) and below (right) -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 sine-wave 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 4.5Vrms (0dBrA) at the output. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at a vanishingly low -140dBRA, or 0.00001%, while the third-order modulation products, at 17kHz and 20kHz, are just above (left) and below (right) -120dBrA, or 0.0001%.

*Diego Estan*

Electronics Measurement Specialist