Link: reviewed by Roger Kanno on *SoundStage! Hi-Fi* on June 15, 2022

**General Information**

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

The SHD Power was conditioned for 1 hour at 1/8th full rated power (~15W into 8 ohms) before any measurements were taken. All measurements were taken with both channels driven, using a 120V/20A dedicated circuit, unless otherwise stated.

The SHD Power is a highly customizable audio component. Beyond its function as an integrated amplifier-DAC, the SHD Power can be utilized as a stand-alone two-channel-in/four-channel-out digital processor with full bass management, parametric equalization, gain trim, and compression. Users can also individually assign any of the four outputs over four different presets. On top of all the output customization, Dirac Live room EQ can be applied to the system as a whole. The SHD Power can be configured using the miniDSP SHD control application (v1.15 was used for these measurements, installed on a Windows 11 laptop, controlling the SHD Power over USB).

The SHD Power has four digital inputs (2x L/R, and labelled Dirac 1 and Dirac 2 in the control app) accessed over S/PDIF (coaxial), S/PDIF TosLink (optical), AES/EBU (XLR), or USB. The SHD Power can also be accessed over LAN (ethernet) and used as streamer using the built-in Volumino platform. The SHD Power has four outputs (or two stereo L/R outputs labeled Output 1 through Output 4 in the control app). The speaker outputs are assigned Output 1 and Output 2; there are two analog sub-outs assigned Output 3 and Output 4; and there are two L/R digital outputs (AES-EBU over XLR), the first assigned Output 1 and Output 2, the second assigned Output 3 and Output 4. Any of the two inputs can be assigned, or “routed” to any output, with gain trim available from +12dB to -72dB in 0.1dB increments. This also includes the option to link outputs for mono configuration. Each output can be low- or high-pass filtered (LPF or HPF) with a customizable slope and cut-off frequency. In addition, a ten-band parametric EQ and a compressor can be applied to each output, and there are four presets available, making for a dizzying number of possibilities. For example, if one wanted to use the SHD Power as a bass-managed integrated amp in a 2.2 channel system, crossed over at 120Hz, for preset 1, one would:

- Select Config 1 in the control application
- Under Routing, route Output 1 (speaker L) to Dirac 1 (input L),
- Route Output 2 (speaker R) to Dirac 2 (input R),
- Route Output 3 (sub out L) to Dirac 1 (input L),
- Route, Output 4 (sub out R) to Dirac 2 (input R),
- Under Outputs, apply a 120Hz (with customizable slope) HPF to Outputs 1 and 2,
- Apply a 120Hz LPF to Outputs 3 and 4

After this, Dirac Live can be applied to the system as a whole using Dirac Live 3, a UMIK-1 microphone, and the SHD Power control application.

For the purposes of these measurements, the coaxial input was used, along with the speaker outputs and analog sub-outs.

Most measurements were made with a standard 0dBFS digital input. Because the SHD Power utilizes a digital amp with a poor damping factor a high frequencies, it also offers an 8/4-ohm switch (in the control software), to optimize frequency response for different speakers. Unless otherwise stated, the switch was left in the 8-ohm position.

Because the SHD Power uses digital-amplifier technology that exhibits considerable noise above 20kHz (see FFTs below), our typical input bandwidth filter setting of 10Hz-90kHz was necessarily changed to 10Hz-22.4kHz for all measurements, except for frequency response and for FFTs. In addition, THD versus frequency sweeps were limited to 6kHz to adequately capture the second and third signal harmonics with the restricted bandwidth setting.

We typically publish the plot of a 10kHz squarewave output for amplifiers. In the case of the SHD Power, a useable output could not be captured using the square-wave input from the APx555, and thus this graph is omitted herein.

Based on the accuracy and repeatable results at various volume levels of the left/right channel matching (see table below), and the lack of analog inputs, the SHD Power volume control is likely applied entirely in the digital domain. The volume control offers a total range of -127.5dB to 0dB on the display, in 0.5dB steps. With the factory defaults, a 0dBFS input will yield 120W into 8 ohms with the volume at maximum (0dB). However, extra gain (up to 12 dB) can be added to any individual preset and output through the miniDSP control software.

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

Volume position | Channel deviation |

-70.0dB | 0.021dB |

-60.0dB | 0.021dB |

-40.0dB | 0.020dB |

-30.0dB | 0.020dB |

-20.0dB | 0.019dB |

-10.0dB | 0.018dB |

0dB | 0.018dB |

**Published specifications vs. our primary measurements**

The table below summarizes the measurements published by miniDSP for the SHD Power compared directly against our own. The published specifications are sourced from miniDSP’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 extended from 10Hz to 500kHz, assume, unless otherwise stated, 10W into 8 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 |

Rated output power into 8 ohms (1% THD, 1kHz) | 120W | 130W |

Rated output power into 4 ohms (1% THD, 1kHz) | 120W | *149W |

THD+N (100Hz, 1W-100W, 8/4 ohms) | <0.005% | 0.002% - 0.008% |

THD+N (20Hz-6kHz, 0.6W-100W, 4 ohms) | <0.03% | <0.05% |

THD+N (20Hz-6kHz, 0.6W-100W, 8 ohms) | <0.07% | <0.05% |

SNR (1kHz, 120W, 8 ohms, A-weighted) | >110dB | 110dB |

Frequency response (24/192, 8 ohms) | 10Hz-30kHz ±0.5dB | 10Hz-30kHz -0.15/+0.7dB |

Crosstalk (1kHz) | <-95dB | -97.1dB |

SNR (line-level output) | 120dB | 119dB |

THD+N (line-level output) | 0.0007% | 0.00035% |

Frequency response (line level output, 24/192) | 10Hz-30kHz ±0.2dB | 10Hz-30kHz -0.15/+0.03dB |

Maximum level (line-level output) | 1.7Vrms | 1.75Vrms |

*auto-shutdown after a few seconds, below 1% THD threshold

Our primary measurements revealed the following using the digital coaxial input (unless specified, assume a 1kHz sinewave at 0dBFS, 10W output, 8-ohm loading, 10Hz to 22.4kHz bandwidth):

Parameter | Left channel | Right channel |

Maximum output power into 8 ohms (1% THD+N, unweighted) | 130W | 130W |

Maximum output power into 4 ohms (1% THD+N, unweighted) | *149W | *149W |

Crosstalk, one channel driven (10kHz, 24/96) | -78.9dB | -79.3dB |

Damping factor | 108 | 107 |

Clipping no-load output voltage | 32.6Vrms | 32.5Vrms |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1, 24/96) | <-65dB | <-66dB |

IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1, 24/96 ) | <-83dB | <-84dB |

IMD ratio (CCIF, 18kHz + 19kHz stimulus tones, 1:1, 16/44.1) | <-65dB | <-66dB |

IMD ratio (SMPTE, 60Hz + 7kHz stimulus tones, 4:1, 16/44.1 ) | <-83dB | <-84dB |

Input sensitivity (for rated power, maximum volume) | **0dBFS | **0dBFS |

Noise level (A-weighted, 24/96) | <101uVrms | <101uVrms |

Noise level (A-weighted, 16/44.1) | <172uVrms | <172uVrms |

Noise level (unweighted, 24/96) | <175uVrms | <175uVrms |

Noise level (unweighted, 16/44.1) | <260uVrms | <255uVrms |

Output Impedance (sub-out) | 1 ohm | 1.2 ohm |

Dynamic range (full rated power, A-weighted, digital 24/96) | 110.4dB | 110.4dB |

Dynamic range (full rated power, A-weighted, digital 16/44.1) | 95.6dB | 95.6dB |

Dynamic range (full rated power, unweighted, digital 24/96) | 105.9dB | 105.9dB |

Dynamic range (full rated power, unweighted, digital 16/44.1) | 93.0dB | 93.1dB |

THD ratio (unweighted, 24/96) | <0.0014% | <0.0014% |

THD ratio (unweighted, 16/44.1) | <0.0014% | <0.0014% |

THD+N ratio (A-weighted, 24/96) | <0.0019% | <0.0017% |

THD+N ratio (A-weighted, 16/44.1) | <0.0025% | <0.0024% |

THD+N ratio (unweighted, 24/96) | <0.0025% | <0.0025% |

THD+N ratio (unweighted, 16/44.1) | <0.0033% | <0.0032% |

Minimum observed line AC voltage | 123.5VAC | 123.5VAC |

*auto-shutdown after a few seconds, below 1% THD threshold

**extra gain can be added via control app

Our typical continuous dynamic power test counld not be performed with the SHD Power due to its lack of analog inputs, and the Audio Precision's lack of a sinewave burst generator using the DAC generator.

**Frequency response vs. input type (8-ohm loading)**

The chart above shows the SHD Power’s frequency response as a function of input type measured across the speaker outputs at 10W into 8 ohms. The blue/red (left/right channels) traces are for a 16-bit/44.1kHz dithered digital input signal from 5Hz to 22kHz using the coaxial digital input, and the purple/green (left/right channels) traces are for a 24/96 dithered digital input signal from 5Hz to 48kHz, while the pink/cyan (left/right channels) traces are for a 24/192 dithered digital input signal from 5Hz to 96kHz.

The 24/96 and 24/192 responses overlap perfectly, indicating 24/192 data is likely downsampled to 24/96. All input data are at -0.15dB at 10Hz, corroborating miniDSP’s claim of 10Hz-30kHz, ±0.5dB. The 16/44.1 data exhibits brick-wall type filtering, with a -3dB point at 21.0kHz. The 24/96 and 24/192 kHz data yielded -3dB points at 45.2kHz. The ±0.5dB claim up to 30kHz is not corroborated, as there is a rise in the response just before 30kHz, peaking at +0.7dB. It should be noted that this response is intentional, because this type of digital amplifier technology exhibits a low damping factor (high output impedance) at high frequencies (see damping factor vs frequency chart below). When frequency response is measured into a 4-ohm load (see RMS level vs. frequency vs load impedance chart below), there is a dip instead of a rise in the response at high frequencies.

**Frequency response (8-ohm loading, with bass management, 24/96 data)**

Above are two frequency-response plots, measured at 10W (8-ohm) at the speaker outputs, and at the line-level subwoofer outputs, with the crossover set at 120Hz, for a 24/96 dithered input signal. The SHD Power crossover uses adjustable slopes. Here, 24dB/octave was chosen. The subwoofer output is essentially flat down to 10Hz.

**Frequency response (4-ohm loading, 4-ohm setting, 24/96 data)**

Above are the frequency-response plots measured at the speaker-level outputs into 4 ohms for a 24/96 dithered input, with the SHD Power speaker impedance setting at 4 ohms. There is a distinct difference between the left (blue) and right (red) channels at high frequencies. The left channel is at about -0.75dB at 20kHz, while the right channel is at roughly 0dB.

**Frequency response (8-ohm loading, Roger Kanno Dirac Live Preset 1, 24/96)**

Above are frequency-response plots measured at the speaker-level outputs into 8 ohms, for a 24/96 dithered input. These show the results with the Dirac Live filter engaged in Roger Kanno’s review, using his PSB Alpha T20 speakers.

**Frequency response (8-ohm loading, Roger Kanno Dirac Live Preset 2, 24/96)**

Above are frequency response plots measured at the speaker-level outputs into 8 ohms, for a 24/96 dithered input. These show the results with the Dirac Live filter engaged in Roger Kanno’s review, using his MartinLogan ESL 9 speakers.

**Frequency response (8-ohm loading, Roger Kanno Dirac Live Preset 3, 24/96)**

Above are frequency response plots measured at the speaker-level outputs into 8 ohms, for a 24/96 dithered input. These show the results with the Dirac Live filter engaged in Roger Kanno’s review, using his MartinLogan ESL 9 speakers and JL Audio E-Sub e112 subwoofers. Note that for this preset, Roger did not apply any bass management, hence the severe cut between 50 and 100Hz, where both the main speakers and subs are reproducing bass.

**Phase response (8-ohm loading, 16/44.1 and 24/96 data)**

Above are the phase response plots from 20Hz to 20kHz, measured across the speaker outputs at 10W into 8 ohms, for a 16/44,1 (blue/red) and 24/96 (purple/green) dithered digital input. The SHD Power does not invert polarity and exhibits, at worst, a little over 20 degrees (at 20Hz for the 16/44.1 data) of phase shift within the audio band.

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

The chart above shows the results of a linearity test for the coaxial digital input for both 16/44.1 (blue/red) and 24/96 (purple/green) input data, measured at the line-level sub-outs of the SHD Power for a 1Vrms (at 0dBFS) output signal. 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. Both data were essentially perfect from 0dBFS to -100dBFS. At -120dBFS, the 16/44.1 data were about +2dB above reference, while the 24/96 data were still perfect. Because of this DAC’s exceptional linearity performance, a second measurement, which we don't usually do, was performed extending down to -140dBFS . . .

. . . which shows the 24/96 data remained within 1dB of flat—a great 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 data)**

The chart 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 line-level sub-outs of the SHD Power. We can see that the SHD Power utilizes a typical sinc function reconstruction filter.

**J-Test (coaxial)**

The chart above shows the results of the J-Test test for the coaxial digital input measured at the line-level sub-outs of the SHD Power. J-Test was developed by Julian Dunn in 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 and below. The test file can also be used in conjunction with artificially injected sine-wave jitter by the Audio Precision, to show how well the DAC rejects jitter.

The coaxial input exhibits low-level peaks throughout the audio-band, at -130dBrA and below. This is a good J-Test result, indicating that the SHD Power DAC likely has strong jitter immunity.

**J-Test (optical)**

The chart above shows the results of the J-Test test for the optical digital input, measured at the line-level sub-outs of the SHD Power. The optical input exhibits low-level peaks throughout the audio band, at -130dBrA and below. As with the coaxial input, this is a good J-Test result, indicating that the SHD Power DAC likely has strong jitter immunity.

**J-Test with 500ns of injected jitter (coaxial)**

Both the coaxial and optical inputs were also tested for jitter immunity by injecting artificial sine-wave jitter at 2kHz, which would manifest as sidebands at 10kHz and 14kHz without any jitter rejection. The results were similar for both inputs, so only the coaxial result is shown. Jitter immunity proved excellent, with no visible sidebands even at a high 500ns of jitter level. At 1000ns of jitter level, the SHD Power DAC lost sync with the input signal.

**Wideband FFT spectrum of white noise and 19.1kHz sine-wave tone (coaxial input)**

The plot above shows a fast Fourier transform (FFT) of the SHD Power’s line-level sub-outs with white noise at -4dBFS (blue/red) and a 19.1kHz sine wave at 0dBFS (1Vrms) fed to the coaxial digital input, sampled at 16/44.1. The sharp roll-off above 20kHz in the white-noise spectrum shows the implementation of a brick-wall-type reconstruction filter. There are no aliased image peaks in the audio band above the -135dBrA noise floor. The main 25kHz alias peak is highly suppressed at -130dBrA. The second and third distortion harmonics (38.2, 57.3kHz) of the 19.1kHz tone are higher, between -100dBrA and -110dBrA.

**RMS level vs. frequency vs. load impedance (1W, left channel only)**

The chart above shows RMS level (relative to 0dBrA, which is 1W into 8 ohms, or 2.83Vrms) as a function of frequency, for the coaxial input with a dithered 24/96 signal swept from 5Hz to 100kHz. The blue plot is into an 8-ohm load, the purple is into a 4-ohm load, the pink plot is an actual speaker (Focal Chora 806, measurements can be found here), and the cyan plot is no load connected. The chart below . . .

. . . is the same but is zoomed in to highlight differences. The most obvious feature in these plots is the significant deviations in response at different loads at high frequencies (above 5kHz or so). This is a characteristic of this type of digital-amplifier technology—there is a rising output impedance (or low damping factor) at high frequencies. This can have the effect of either brightening or dulling the treble response in a system, depending on the characteristic impedance of the speaker. It must be pointed out that, in the case of the SHD Power, this is not an issue, given that one of the primary reasons for purchasing this device is to compensate for in-room frequency response aberrations through the built-in parametric EQ and/or Dirac Live room correction systems. In the flatter part of curves (below 5kHz), we can see a maximum deviation within the audio band of about 0.15dB from 4 ohms to no load, which is an indication of a mid-level damping factor. The maximum variation in RMS level when a real speaker was used in the flat portion of the curve is a little less, deviating by about 0.1dB.

**THD ratio (unweighted) vs. frequency vs. output power (24/96 data)**

The chart above shows THD ratios at the output into 8 ohms as a function of frequency for a 24/96 dithered sine-wave stimulus at the coaxial input. The blue and red plots are for left and right channels at 1W output into 8 ohms, purple/green at 10W, and pink/orange, just below the rated 120W. The power was varied using the volume control. The 1 and 10W are very similar, ranging from about 0.001% from 20Hz through to 1kHz, then up to 0.005-0.01% at 6kHz. The 120W data yielded higher results, but still admirably low, at about 0.005% from 20Hz to 600Hz, then up to 0.05% at 6kHz. At low frequencies, the left channel outperformed the right channel at 120W by as much as 5dB.

**THD ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms (24/96 data)**

The chart above shows THD ratios measured at the output of the SHD Power as a function of output power for a 24/96 dithered sine-wave stimulus at the coaxial input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). The 8-ohm data generally outperformed the 4-ohm data by almost 10dB, from 1W to the “knee” at just past 100W. At low output power, THD ratios were as high as 0.05% to 0.2% at 50mW. From 1W to roughly 100W, THD ratios for the 8-ohm data ranged from 0.001% to 0.005%, and 0.002% to 0.01% for the 4-ohm data. The 1% THD mark was reached for the 8-ohm data at 130W. We could not reach the 1% THD level with a 4-ohm load without tripping the protection circuit. The highest sustainable power output we measured was 149W, but only for a few seconds before the unit shut down.

**THD+N ratio (unweighted) vs. output power at 1kHz into 4 and 8 ohms (24/96 data)**

The chart above shows THD+N ratios measured at the output of the SHD Power as a function of output power for a 24/96 dithered sine-wave stimulus at the coaxial input, for an 8-ohm load (blue/red for left/right channels) and a 4-ohm load (purple/green for left/right channels). The 8-ohm data generally outperformed the 4-ohm data by 5-10dB, from 10W to the “knee” at just past 100W. At low output power, THD+N ratios were as high as 0.1% to 0.2% at 50mW. From 1W to roughly 100W, THD+N ratios for the 8-ohm data ranged from 0.005% to as low as 0.002% (at 20-30W), and 0.005% to 0.01% for the 4-ohm data.

**THD ratio (unweighted) vs. frequency at 8, 4, and 2 ohms (left channel only, 24/96 data)**

The chart above shows THD ratios measured at the output of the SHD Power as a function of frequency into three different loads (8/4/2 ohms), for a 24/96 dithered sine-wave stimulus at the coaxial input that yields 10W at the output into 8 ohms (and roughly 20W into 4 ohms, and 40W into 2 ohms). The 8-ohm load is the blue trace, the 4-ohm load the purple trace, and the 2-ohm load the pink trace. We find increasing THD values from 8 to 4 to 2 ohms. Into 8 ohms, THD ratios are at or just below 0.001% from 20Hz to 500Hz and up to 0.008% at 4kHz. The 4-ohm THD ratios are between 3 and 10dB higher through most of the frequency range, and the 2-ohm data, about 10dB higher than the 4-ohm data. Even into 2 ohms, the SHD Power manages THD ratios between 0.003% and 0.05% at 40W.

**THD ratio (unweighted) vs. frequency into 8 ohms and real speakers (left channel only, 24/96 data)**

The chart above shows THD ratios measured at the output of the SHD Power as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for a 24/96 dithered sine-wave stimulus at the coaxial input. The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). At high frequencies (5-6kHz), the dummy load and three-way speaker track closely, while the two-way speaker yielded lower results by a smuch as 15dB at 3-4kHz. Below 1kHz, there are significant diffrences in THD ratios between the dummy load and real speakers, by as much as 40dB at 20Hz, where the two-way speaker THD ratio was 0.1% comapred to the 0.001% measured across the dummy load. The amplifier section of the SHD Power seems to be sensitive to load variations in terms of THD.

**IMD ratio (CCIF) vs. frequency into 8 ohms and real speakers (left channel only, 24/96 data)**

The chart above shows intermodulation distortion (IMD) ratios measured at the output of the SHD Power as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for a 24/96 dithered sine-wave stimulus at the coaxial input. Here the CCIF IMD method is used, where the primary frequency is swept from 20kHz (F1) down to 2.5kHz, and the secondary frequency (F2) is always 1kHz lower than the primary, with a 1:1 ratio. The CCIF IMD analysis results are the sum of the second (F1-F2 or 1kHz) and third modulation products (F1+1kHz, F2-1kHz). The 8-ohm load is the blue trace, the purple plot is a two-way speaker (Focal Chora 806, measurements can be found here), and the pink plot is a three-way speaker (Paradigm Founder Series 100F, measurements can be found here). Here again we see variations between the dummy load, which yielded the lowest IMD results between 0.002% at 2.5kHz and 0.025% at 20kHz, and the real speakers, where the 3-way speaker was 15dB higher at 4-5kHz. The two-way speaker yielded IMD results between the dummy load and three-way speaker.

**IMD ratio (SMPTE) vs. frequency into 8 ohms and real speakers (left channel only, 24/96 data)**

The chart above shows IMD ratios measured at the output of the SHD Power as a function of frequency into an 8-ohm load and two different speakers for a constant output voltage of 2.83Vrms (1W into 8 ohms) for a 24/96 dithered sine-wave stimulus at the coaxial input. Here, the SMPTE IMD method is used, where the primary frequency (F1) is swept from 250Hz down to 40Hz, and the secondary frequency (F2) is held at 7kHz with a 4:1 ratio. The SMPTE IMD analysis results consider the second (F2 ± F1) through the fifth (F2 ± 4xF1) modulation products. Here all three data sets are fairly close together, between 0.005% and 0.01% from 40Hz to 250Hz. The three-way speaker did yield results about 5dB higher than the 2-way speaker and dummy load between 80Hz and 250Hz.

**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 output across an 8-ohm load at 10W for the coaxial digital input, sampled at 16/44.1. Here we find the second (2kHz) and third (3kHz) harmonic of the signal at just below -100/-105dBrA (left/right), or 0.001/0.0006%. Higher order signal harmonics are visible at -110dBrA, or 0.0003%, and below. The noise-related peaks on the left side of the signal peak are virtually non-existent.

**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 output across an 8-ohm load at 10W for the coaxial digital input, sampled at 24/96. The FFT spectrum is nearly identical within the audio band to the 16/44.1 FFT above, but for a slightly lower noise floor due to the 24-bit depth.

**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 sine-wave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. We see the 1kHz primary signal peak, at the correct amplitude, and signal harmonics are non-existent above the 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 sine-wave stimulus at the coaxial digital input, measured at the output across an 8-ohm load. The FFT spectrum is nearly identical within the audio band to the 16/44.1 FFT above.

**FFT spectrum – 50Hz (digital input, 24/96 data at 0dBFS)**

Shown above is the FFT for a 50Hz input sine-wave stimulus measured at the output across an 8-ohm load at 10W for a 24/96 dithered sine-wave stimulus at the coaxial input. The X axis is zoomed in from 40Hz to 1kHz, so that peaks from noise artifacts can be directly compared against peaks from the harmonics of the signal. The second (100Hz) harmonic dominates at -100/-105dBrA (left/right), or 0.001/0.0006%, but even and odd signal harmonics at lower levels (below -120dBrA, or 0.0001%) can be seen throughout.

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

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 16/44.1. We find that the second-order modulation product (*i.e.*, the difference signal of 1kHz) is at 105/110dBrA (left/right channels), or 0.0006/0.0003%. The third-order modulation products, at 17kHz and 20kHz, are around -75dBrA, or 0.02%. We also see the main aliased peaks at 25.1kHz and 26.1kHz around -70dBrA due to the 44.1kHz sample rate (*e.g.*, 44.1kHz-19kHz = 25.1kHz).

**Intermodulation distortion FFT (18kHz + 19kHz summed stimulus, coaxial digital input, 24/96 data)**

Shown above is an FFT of the intermodulation distortion (IMD) products for an 18kHz + 19kHz summed sine-wave stimulus tone measured at the output across an 8-ohm load at 10W for the digital coaxial input at 24/96. The FFT spectrum is nearly identical within the audio band to the 16/44.1 FFT above.

**FFT spectrum of 400kHz switching frequency relative to a 1kHz tone (24/96 data)**

The SHD Power’s amplifier relies on a switching oscillator to convert the input signal to a pulse-width modulated (PWM) square wave (on/off) signal before sending the signal through a low-pass filter to generate an output signal. The SHD Power’s oscillator switches at a rate of about 450kHz, and this graph plots a wide bandwidth FFT spectrum of the amplifier’s output at 10W into 8 ohms as it’s fed a 1kHz dithered 24/96 sine wave. We can see that the 400kHz peak is quite evident, and at -30dBrA. There is also a peak at 900kHz (the second of the 400kHz peak), at -60dBrA. Those three peaks—the fundamental and its harmonics—are direct results of the switching oscillators in the SHD Power’s amp modules. The noise around those very-high-frequency signals are in the signal, but all that noise is far above the audio band—and therefore inaudible—and so high in frequency that any loudspeaker the amplifier is driving should filter it all out anyway.

**Damping factor vs. frequency (20Hz to 20kHz)**

The final graph above is the damping factor as a function of frequency. Both channels track closely and show a constant damping factor right around 110 from 20Hz to about 600Hz. Above this point, the damping factor decreases sharply, hitting a low of about 11 at 20kHz.

*Diego Estan*

Electronics Measurement Specialist