Link: reviewed by Matt Bonaccio on *SoundStage! Hi-Fi* on February 15, 2024

**General Information**

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

The Ferrum Audio Wandla was conditioned for 30 minutes at 0dBFS/4Vrms out (2Vrms unbalanced output) into 200k ohms before any measurements were taken.

The Wandla offers one analog line-level input (RCA) and several digital inputs (S/PDIF over coaxial RCA and optical, AES-EBU, I2S over HDMI, and asynchronous over USB). There are both unbalanced (RCA) and balanced (XLR) outputs. For the purposes of these measurements, unless otherwise stated, the following inputs were evaluated using the balanced XLR outputs: digital coaxial S/PDIF (RCA), analog unbalanced (RCA). Comparisons were made between unbalanced (RCA) and balanced (XLR) line outputs, and lower THD and an extra 6dB of gain were seen using the XLR outputs (FFTs for different configurations can be seen in this report).

Unless noted, the measurements were performed with the stock power supply. Where noted, additional measurements were performed with the optional Ferrum Audio Hypsos power supply.

The Wandla offers two different types of volume control: analog and digital. Unless otherwise stated, the analog volume control was used. Using digital inputs, at the maximum volume, the Wandla can output just over 10Vrms (XLR).

There are also a few options available through the user menu. Unless otherwise stated the following was used by default:

- Filter: HQ Gauss (also available: HQ Apod, HQ Apod MP, HQ short, ESS Lin-Ph)
- Bypass: off
- Theatre bypass: off
- Output balance: C
- Digital input trim: 0dB
- Analog input gain: 0dB (-12dB to 12dB available)

Most measurements were made with a 2Vrms line-level and 0dBFS digital input with the volume set to achieve 4Vrms at the balanced output (100 for analog, 92 for digital).

Based on the accuracy and random results of the left/right volume channel matching (see table below), the Wandla analog volume control is likely digitally controlled in the analog domain. The Wandla offers 100 volume steps from -93dB to 5.8dB for the line-level analog inputs and balanced outputs. For a 0dBFS digital input, the XLR outputs ranged from 102uVrms (volume 1) to 10.2Vrms (volume 100). All steps are in 1.0dB increments.

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

Volume position | Channel deviation |

1 | 0.05dB |

10 | 0.136dB |

20 | 0.077dB |

30 | 0.033dB |

40 | 0.059dB |

50 | 0.05dB |

60 | 0.002dB |

70 | 0.067dB |

80 | 0.014dB |

90 | 0.022dB |

100 | 0.034dB |

**Published specifications vs. our primary measurements**

The table below summarizes the measurements published by Ferrum Audio for the Wandla compared directly against our own. The published specifications are sourced from Ferrum’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 was set at its maximum (DC to 1MHz), assume, unless otherwise stated, 4Vrms output (XLR) into 200k ohms and a measurement input bandwidth of 10Hz to 22.4kHz, and the worst-case measured result between the left and right channels.

Parameter | Manufacturer | SoundStage! Lab |

Analog input max voltage | 9.5Vrms | 10.15Vrms |

Input impedance (line level, RCA) | 47k ohms | 52.4k ohms |

Output level (digital, 0dBFS, max volume, XLR) | 9.3Vrms | 10.2Vrms |

Output level (digital, 0dBFS, max volume, RCA) | 4.65Vrms | 5.1Vrms |

Frequency response (line-level) | 10Hz-200kHz (±0.1dB) | 5Hz-200kHz (±0.05dB) |

DAC THD (1kHz) | -121dB | -122dB |

DAC THD+N (1kHz, 20Hz-20kHz bandwidth) | -115dB | -112dB |

Analog input THD (2/4Vrms out RCA/XLR) | -123dB | -120dB |

Dynamic range (analog in, A-wgt, 20Vrms out) | 127dB | 126dB |

Dynamic range (digital in, 24/96, A-wgt, 10Vrms out) | 127dB | 122dB |

Crosstalk (1kHz) | -120dB | -134dB |

Output impedance (RCA) | 22 ohms | 22.8 ohms |

Output impedance (XLR) | 44 ohms | 44.5 ohms |

Our primary measurements revealed the following using the balanced line-level analog input and digital coaxial input (unless specified, assume a 1kHz sinewave at 2Vrms or 0dBFS, 4Vrms output (XLR), 200kohm loading, 10Hz to 22.4kHz bandwidth):

Parameter | Left channel | Right channel |

Crosstalk, one channel driven (10kHz, analog in) | -116.9dB | -121.9dB |

Crosstalk, one channel driven (10kHz, digital in 24/96) | -139.5dB | -133.6dB |

DC offset | <0.01mV | <0.12mV |

Gain (RCA in/out, default) | -0.2dB | -0.2dB |

Gain (RCA in/XLR out, default) | 5.8dB | 5.8dB |

Gain (RCA in/out, max) | 11.8dB | 11.8dB |

Gain (RCA in/XLR out, max) | 17.8dB | 17.8dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1) | <-111dB | <-112dB |

IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1 ) | <-105dB | <-106dB |

Input impedance (line input, RCA) | 52.4k ohms | 52.4k ohms |

Maximum output voltage (at clipping 1% THD+N, XLR) | 19.7Vrms | 19.7Vrms |

Maximum output voltage (at clipping 1% THD+N into 600 ohms, XLR) | 15.9Vrms | 15.9Vrms |

Maximum output voltage (at clipping 1% THD+N, RCA) | 9.9Vrms | 9.9Vrms |

Maximum output voltage (24/96 0dBFS, XLR) | 10.2Vrms | 10.2Vrms |

Maximum output voltage (24/96 0dBFS, RCA) | 5.1Vrms | 5.1Vrms |

Noise level (with signal, A-weighted) | <8uVrms | <9uVrms |

Noise level (with signal, 20Hz to 20kHz) | <10uVrms | <11uVrms |

Noise level (no signal, A-weighted, volume min) | <6.3uVrms | <6.3uVrms |

Noise level (no signal, 20Hz to 20kHz, volume min) | <8uVrms | <8uVrms |

Noise level (no signal, A-weighted, volume min, RCA) | <3.64uVrms | <3.64uVrms |

Noise level (with signal, A-weighted, 24/96) | <7.4uVrms | <7.4uVrms |

Noise level (with signal, 20Hz to 20kHz, 24/96) | <9.4uVrms | <9.4uVrms |

Output Impedance (RCA) | 22.8 ohms | 22.8 ohms |

Output Impedance (XLR) | 44.4 ohms | 44.5 ohms |

Signal-to-noise ratio (4Vrms out, A-weighted, 2Vrms in) | 113.7dB | 112.3dB |

Signal-to-noise ratio (4Vrms out, 20Hz to 20kHz, 2Vrms in) | 111.8dB | 110.7dB |

Signal-to-noise ratio (4Vrms out, A-weighted, max volume) | 113.7dB | 112.3dB |

Dynamic Range (4Vrms out, A-weighted, digital 24/96) | 115.1dB | 115.1dB |

Dynamic Range (4Vrms out, A-weighted, digital 16/44.1) | 96.0dB | 96.0dB |

THD ratio (unweighted) | <0.00011% | <0.00011% |

THD ratio (unweighted, digital 24/96) | <0.00008% | <0.00008% |

THD ratio (unweighted, digital 16/44.1) | <0.00035% | <0.00035% |

THD+N ratio (A-weighted) | <0.00023% | <0.00026% |

THD+N ratio (A-weighted, digital 24/96) | <0.0002% | <0.0002% |

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

THD+N ratio (unweighted) | <0.00031% | <0.00033% |

**Frequency response (line-level input)**

In our measured frequency-response (relative to 1kHz) plot above, the Wandla is perfectly flat within the audioband (0dB at 20Hz and 20kHz). At the extremes, the Wandla is 0dB at 5Hz and 0dB at 205kHz (the maximum allowable frequency by the signal generator). Deviations between 5Hz and 200kHz are within +/-0.05dB. These data corroborate Ferrum’s claim of 10Hz to 200kHz (+/-0.1dB). The Wandla appears to be DC-coupled, as there is no attenuation at low frequencies, even at 5Hz. It is also appropriate to say that the Wandla is a very high-bandwidth audio device. In the graph above and most of the graphs below, only a single trace may be visible. This is because the left channel (blue or purple trace) is performing identically to the right channel (red or green trace), and so they perfectly overlap, indicating that the two channels are ideally matched.

**Phase response (line-level input)**

Above is the phase response plot from 20Hz to 20kHz for the balanced line=level input. The Wandla does not invert polarity and exhibits essentially no phase shift within the audioband.

**Frequency response vs. input type**

The chart above shows the Wandla’s frequency response (relative to 1kHz) as a function of input type. The dark green trace is the same (but limited to 80kHz) analog input data from the previous graph. The blue trace is for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial input, the purple trace is for a 24/96 dithered digital input signal from 5Hz to 48kHz, and finally pink is 24/192 from 5Hz to 96kHz. The behavior at low frequencies is the same for all the digital sample rates, as well as the analog input - flat down to 5Hz. The behavior at high frequencies for all three digital sample rates is as expected, offering filtering around 22k, 48k, and 96kHz (half the respective sample rate). The 44.1kHz sampled input signal exhibits typical “brickwall”-type behavior, with a -3dB point at 20.3kHz. The -3dB point for the 96kHz sampled data is at 44kHz, and 67kHz for the 192kHz sampled data.

**Frequency response vs. filter type (16/44.1; HQ Gauss, HQ Apod, HQ Apod MP)**

The chart above shows the frequency response (relative to 1kHz) as a function of filter type for a 16/44.1 0dBFS digital input. The blue trace is for the HQ Gauss filter, red for HQ Apod filter, and green for HQ Apod MP filter. All three behaved the same, with brickwall-type behavior and a -3dB point at 20.3kHz.

**Frequency response vs. filter type (16/44.1; HQ short, ESS Lin-Ph)**

The chart above shows the frequency response (relative to 1kHz) as a function of filter type for a 16/44.1 0dBFS digital input. The blue trace is for the HQ Short filter, red for ESS Lin-Ph filter. The HQ Short filter exhibits softer attenuation around the corner frequency, with a -3dB point just shy of 20kHz, while the ESS Lin-Ph filter exhibits more brickwall-type behavior with a -3dB point of 21kHz.

**Phase response vs. filter type (16/44.1; HQ Gauss, HQ Apod, HQ Apod MP)**

Above is the phase response plot from 20Hz to 20kHz as a function of filter type for a 16/44.1 0dBFS digital input. The blue trace is for the HQ Gauss filter, red for HQ Apod, and green for HQ Apod MP. Both the HQ Gauss and HQ Apod filters exhibit essentially no phase shift within the audioband. The HQ Apod MP filter is at -180 degrees at 17kHz.

**Phase response vs. filter type (16/44.1; HQ short, ESS Lin-Ph)**

Above is the phase-response plot from 20Hz to 20kHz as a function of filter type for a 16/44.1 0dBFS digital input. The blue trace is for the HQ Short filter, red for ESS Lin-Ph. Both the HQ Short and ESS Lin-Ph filters exhibit essentially no phase shift within the audioband.

**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 outputs of the Wandla. 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 would be a straight flat line at 0dB. At -120dBFS, the 16/44.1 data overshot by only 1-2dB, while the 24/96 remained perfect. To verify how well the 24/96 data would perform down to -140dBFS, we extended the sweep in the chart below.

Here we can see that the 24/96 data only overshot the mark by +4.5/+2dB (left/right) at -140dBFS. This is an exceptional digital linearity test result.

**Impulse response vs. filter type (24/44.1; HQ Gauss, HQ Apod, HQ Apod MP) (24/48 data)**

The graph above shows the impulse response 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, measured at the balanced outputs of the Wandla. The blue trace is for the HQ Gauss filter, red for HQ Apod and green for HQ Apod MP. The HQ Gauss and HQ Apod filters behave like typical symmetrical sinc functions. The HQ Apod MP filter shows no pre-ringing but long post-ringing.

**Impulse response vs. filter type (16/44.1; HQ short, ESS Lin-Ph) (24/48 data)**

The graph above shows the impulse response 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, measured at the balanced outputs of the Wandla. The blue trace is for the HQ Short filter, red for ESS Lin-Ph. Both filters behave like typical symmetrical sinc functions, but with less pre-/post-ringing compared to the HQ Gauss and HQ Apod filters above.

**J-Test (coaxial input)**

The chart above shows the results of the “-Test test for the coaxial digital input measured at the line-level balanced output of the Wandla. J-Test was developed by Julian Dunn the 1990s. It is a test signal—specifically, a -3dBFS undithered 12kHz squarewave sampled (in this case) at 48kHz (24 bits). Since even the first odd harmonic (i.e., 36kHz) of the 12kHz squarewave 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 squarewave 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 and below. The test file can also be used in conjunction with artificially injected sinewave jitter by the Audio Precision, to show how well the DAC rejects jitter.

The coaxial S/PDIF input of the Wandla shows essentially a perfect J-Test result, with no peaks (other than signal peaks: 12kHz and 250/750Hz) visible above the -160dBrA noise floor.

**J-Test (optical input)**

The chart above shows the results of the J-Test test for the optical digital input measured at the balanced outputs of the Wandla. The results are the same as the coaxial input.

**J-Test (AES-EBU input)**

The chart above shows the results of the J-Test test for the AES-EBU digital input measured at the balanced outputs of the Wandla. The results are the same as the coaxial and optical inputs.

**J-Test (coaxial, 2kHz sinewave jitter at 100ns)**

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level output of the Wandla, with an additional 100ns of 2kHz sinewave jitter injected by the APx555. The results are as the pristine J-Test would predict—visible but highly suppressed (-140dBrA) peaks at the 10kHz and 14kHz positions.

**Wideband FFT spectrum of white noise and 19.1kHz sinewave tone (HQ Gauss filter, coaxial input)**

The chart above shows a fast Fourier transform (FFT) of the Wandla’s balanced outputs with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1, using the HQ Gauss filter. The steep roll-off around 20kHz in the white noise spectrum shows the use of a brick-wall type reconstruction filter. There are no obvious aliased images within the audio band. The primary aliasing signal at 25kHz is also completely suppressed, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz are below -110dBrA.

**Wideband FFT spectrum of white noise and 19.1kHz sinewave tone (HQ Apod MP filter, coaxial input)**

The chart above shows a fast Fourier transform (FFT) of the Wandla’s balanced outputs with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1, using the HQ Apod filter. We see essentially the same FFT as with the HQ Gauss filter above.

**Wideband FFT spectrum of white noise and 19.1kHz sinewave tone (HQ Apod MP filter, coaxial input)**

The chart above shows a fast Fourier transform (FFT) of the Wandla’s balanced outputs with white noise at -4 dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1, using the HQ Apod MP filter. We see essentially the same FFT as with the HQ Gauss and HQ Apod MP filters above.

**Wideband FFT spectrum of white noise and 19.1kHz sinewave tone (HQ Short filter, coaxial input)**

The chart above shows a fast Fourier transform (FFT) of the Wandla’s balanced outputs with white noise at -4dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1, using the HQ Short filter. Here the roll-off around 20kHz in the white-noise spectrum is shallower compared to the first three filters. There is also a little bit of attenuation in the main peak at 19.1kHz, not quite reaching 0dBrA. There are no obvious aliased images within the audioband. The primary aliasing signal at 25kHz is also completely suppressed, while the second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz are below -110dBrA.

**Wideband FFT spectrum of white noise and 19.1kHz sinewave tone (ESS Lin-Ph filter, coaxial input)**

The chart above shows a fast Fourier transform (FFT) of the Wandla’s balanced outputs with white noise at -4 dBFS (blue/red) and a 19.1 kHz sinewave at 0dBFS fed to the coaxial digital input, sampled at 16/44.1, using the ESS Lin-Ph filter. We see essentially the same FFT as with the HQ Short filter above.

**THD ratio (unweighted) vs. frequency vs. load (analog)**

The chart above shows THD ratios at the balanced line-level output into 200k ohms (blue/red) and 600 ohms (purple/green) for an analog 2Vrms input as a function of frequency. The 200k ohms and 600 ohms data are close but not identical. THD ratios are very low, from 0.0001% from 20Hz to 1kHz for the 200k ohm load, then rising up to 0.0004% at 20kHz. Into 600 ohms, between 20Hz and 1kHz, THD ratios were roughly 5dB higher.

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

The chart above shows THD ratios at the balanced line-level output into 200k ohms (blue/red) and 600 ohms (purple/green) for a 24/96 0dBFS input as a function of frequency. The 200k ohms and 600 ohms data are close but not identical. THD ratios are extraordinarily low, from 0.00006% to 0.0001% from 20Hz to 1kHz for the 200k ohm load, then rising up to 0.0002% at 20kHz. Into 600 ohms, between 20Hz and 2kHz, THD ratios were roughly 5dB higher.

**THD ratio (unweighted) vs. frequency vs. load (digital 24/96, Hypsos power supply)**

The chart above shows THD ratios at the balanced line-level output into 200k ohms (blue/red) and 600 ohms (purple/green) for a 24/96 0dBFS input as a function of frequency. This time the Hypsos power supply was used. The pink/orange traces are with the Hypsos using the maximum 30V output, while purple/green is the standard 24V, both into 600 ohms. We find that using the upgraded power supply had no effect on THD ratios into 600 ohms.

**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 for a 16/44.1 (blue/red) dithered 1kHz signal at the coaxial input and a 24/96 (purple/green) signal, as a function of frequency. The 16/44.1 THD ratios were higher, although this is due to the higher 16-bit noise floor and limited averaging times for each measurement. The long FFTs (below) show that 16/44.1 and 24/96 data yield the same THD results. THD ratios are extraordinarily low for the 24/96 data, from 0.00006% to 0.0001% from 20Hz to 1kHz for the 200k ohm load, then rising up to 0.0002% at 20kHz.

**THD ratio (unweighted) vs. output (analog)**

The chart above shows THD ratios measured at the balanced outputs of the Wandla as a function of output voltage for the unbalanced line-level input. THD values start at 0.1% at 1mVrms, down to a low of just below 0.0001% at 3Vrms, then a steep rise past 5Vrms to the 1% THD mark at 20Vrms.

**THD+N ratio (unweighted) vs. output (analog)**

The chart above shows THD+N ratios measured at the balanced outputs of the Wandla as a function of output voltage for the unbalanced line-level input. THD+N values start at 1% at 1mVrms, down to a low of just below 0.0003% at 5-7Vrms, then a steep rise past 5Vrms to the 1% THD mark at 20Vrms.

**THD ratio (unweighted) vs. output (16/44.1 and 24/96)**

The chart above shows THD ratios measured at the balanced outputs of the Wandla as a function of output voltage for the digital coaxial S/PDIF input, swept from -90dBFS to 0dBFS, with the volume control at maximum. Blue/red traces are for 16/44.1 data, and purple/green for 24/96. For the 16/44.1 data, THD values start at 3%, and predictably, reach their low at the maximum output voltage of about 10Vrms, at 0.0003%. For the 24/96 data, THD ratios ranged from 0.2% down to 0.0001% at the maximum output voltage. The 16/44.1 THD ratios were higher, although this is due to the higher 16-bit noise floor and limited averaging times for each measurement. The long FFTs (below) show that 16/44.1 and 24/96 data yield the same THD results.

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

The chart above shows THD+N ratios measured at the balanced outputs of the Wandla as a function of output voltage for the digital coaxial S/PDIF input, swept from -90dBFS to 0dBFS, with the volume control at maximum. Blue/red traces are for 16/44.1 data, and purple/green for 24/96. For the 16/44.1 data, THD+N values start at 20%, and predictably, reach their low at the maximum output voltage of about 10Vrms, at 0.002%. For the 24/96 data, THD ratios ranged from 1.5% down to 0.00015% at the maximum output voltage.

**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 balanced output for 16/44.1 (blue/red) input data and 24/96 input data (purple/green), from -60dBFS to 0dBFS. 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 16/44.1 data yields IMD ratios from 2% down to 0.003% at 0dBFS. The 24/96 data yields IMD ratios from 0.2% down to 0.0004% near 0dBFS.

**FFT spectrum – 1kHz (XLR output, line-level input)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the balanced outputs for the unbalanced line-level input. We see that the signal’s second harmonic, at 2kHz, is just below -120dBrA or 0.0001%, and -130dBrA, or 0.00003%, at the third (3kHz) harmonic. The subsequent signal harmonics are around the very low -140dBrA, or 0.00001%, level. Below 1kHz, we see a hint of a peak at 60Hz, but at -150dBrA, or 0.000003%.

**FFT spectrum – 1kHz (RCA output, line-level input)**

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the unbalanced outputs for the unbalanced line-level input. We see that the main difference is that the RCA outputs yield higher THD compared to the XLR outputs, with the second (2kHz) harmonic at the -110dBrA, or 0.0003%, level.

**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 outputs for the coaxial digital input, sampled at 16/44.1. We see that both the second (2kHz) and third (3kHz) signal harmonics are just above the -130dBrA, or 0.00003%, level. The noise floor is much higher due to the 16-bit depth limitation.

**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 outputs for the coaxial digital input, sampled at 24/96. We see that both the second (2kHz) and third (3kHz) signal harmonics are just above the -130dBrA, or 0.00003%, level. With the lower noise floor due to the 24-bit depth, we can see higher-order signal harmonics just above and below the -140dBrA, or 0.00001%, level. There as zero noise-related peaks to be seen above the -155dBrA noise floor.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the balanced outputs for the coaxial digital input, sampled at 24/96, but using the digital volume control (set to the same value of 92 to achieve 4Vrms at the output). Although this FFT is still relatively clean and similar to the FFT above where the analog volume control was used, it’s not as clean. Signal harmonics here reach almost -120dBrA, or 0.0001%, at 3/5/7kHz. There is no difference in terms of power-supply-related noise.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the unbalanced outputs for the coaxial digital input, sampled at 24/96. We a similar FFT compared to the 24/96 balanced output FFT, but for a higher second (2kHz) signal harmonic peak here at almost -110dBrA, or 0.0003%.

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

Shown above is the fast Fourier transform (FFT) for a 1kHz input sinewave stimulus, measured at the balanced outputs for the coaxial digital input, sampled at 24/96, but with the external Hypsos power-supply. We can see that this FFT is essentially identical to the 24/96 FFT above using the stock power-supply and balanced output.

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

Shown above is the FFT for a 1kHz -90dBFS dithered 16/44.1 input sinewave stimulus at the coaxial digital input, measured at the balanced outputs. We see the 1kHz primary signal peak, at the correct amplitude, and no signal or noise related harmonic peaks above the -140dBrA noise floor.

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

Shown above is the FFT for a 1kHz -90dBFS dithered 24/96 input sinewave stimulus at the coaxial digital input, measured at the balanced outputs. We see the 1kHz primary signal peak, at the correct amplitude, and no signal or noise related peaks above the -155dBrA noise floor.

**FFT spectrum – 50Hz (line-level input)**

Shown above is the FFT for a 50Hz input sinewave stimulus measured at the balanced outputs for the unbalanced line-level input. The X axis is zoomed in from 40 Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The most predominant (non-signal) peaks are that of the signal’s second (100Hz) harmonic at -120dBrA or 0.0001%, and the third signal harmonic (150Hz) at -130dBrA or 0.00003%. A small power-supply-related peak can be seen at 60Hz at -140dBrA, or 0.00001%, but this is inherent to the Audio Precision sinewave generator.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, line-level input)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sinewave stimulus tone measured at the balanced outputs for the unbalanced line-level input. The input RMS values are set at -6.02dBrA so that, if summed for a mean frequency of 18.5kHz, would yield 4Vrms at the output. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -120dBRA, or 0.0001%, while the third-order modulation products, at 17kHz and 20kHz, are at around -130dBrA, or 0.00003%. This is a very clean IMD result.

**Intermodulation distortion FFT (line-level input, APx 32 tone)**

Shown above is the FFT of the balanced outputs of the Wandla with the APx 32-tone signal applied to the analog unbalanced input. The combined amplitude of the 32 tones is the 0dBrA reference, and corresponds to 4Vrms. The intermodulation products—i.e., the “grass” between the test tones—are distortion products from the amplifier and are around the extremely low -150dBrA, or 0.000003%, level.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 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 outputs for the digital coaxial input at 16/44.1. We find that the second-order modulation product (i.e., the difference signal of 1kHz) cannot be seen above the -140dBrA, or 0.00001%, noise floor, while the third-order modulation products, at 17kHz and 20kHz, are at -130dBrA, or 0.00003%.

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 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 outputs for the digital coaxial input at 24/96. We find that the second-order modulation product (i.e., the difference signal of 1kHz) is at -140dBrA, or 0.00001%, while the third-order modulation products, at 17kHz and 20kHz, are at -130dBrA, or 0.00003%. This is an exquisitely clean IMD result.

**Square-wave response (10kHz)**

Above is the 10kHz squarewave response using the analog line-level input, at roughly 4Vrms at the balanced output. Due to limitations inherent to the Audio Precision APx555 B Series analyzer, this graph should not be used to infer or extrapolate the Wandla’s slew-rate performance. Rather, it should be seen as a qualitative representation of its extremely extended bandwidth. An ideal squarewave can be represented as the sum of a sinewave and an infinite series of its odd-order harmonics (e.g., 10kHz + 30kHz + 50kHz + 70kHz . . .). A limited bandwidth will show only the sum of the lower-order harmonics, which may result in noticeable undershoot and/or overshoot, and softening of the edges. The Wandla’s reproduction of the 10kHz square wave is essentially perfect, with sharp corners and no overshoot/undershoot.

*Diego Estan*

Electronics Measurement Specialist