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DDJ-400 Measurments

kipman725

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Intro:​

The DDJ-400 is an entry level DJ controller with master out (consumer line level single ended) and headphone out. Most of the functionality is through the REKORDBOX software with almost all controls and audio processing within that software with the exception of the Master level control. My controller is modified from stock in that the I2S lines to the DAC are also connected to an SPDIF/AES output board I have mounted internally to bypass the DAC. I don't think this will affect the DAC output as the twisted pairs to the SPDIF board are connected via 100ohm resistors but performance degradation is possible from this modification and I would like to check my results with a stock unit. The Firmware is the latest 1.03.

1640880370744.png

Tests have been conducted using my TASCAM US-2x2HR interface which you can see loopback of here. Mostly test tones (pink, 1kHz Sine) have been generated and are played back from Rekordbox 6.5.3 unless otherwise stated.

Output levels and THD+N:​

Clipping test:​

Mixer headroom set to NONE, 0dBFs sine wave on Deck 1, Master output set to FULL channel trim at +9dB, 2.239Vrms left channel, 2.234Vrms right channel (limiter has engaged), -13.4dBfs on input meters (9.22dBu).

1640880407543.png

Setting Mixer headroom to 9dB results in almost the same level of 8.45dBu suggesting we are running into Rekordbox limiter.

THD+1 1kHz normal output:​

Setting trim to mid point (0dB) and keeping output level at full and 9dB mixer headroom reduces level to -0.26dBu (752mV) the top red level light on the channel level meter on the controller is no longer lit. This seems an appropriate setting to use the controller in as the level has reduced by ~9dB as the trim setting indicates and so we are confident we have the specified mixer headroom before limiting.

1640880433928.png


Noise dominated (spurs of fundamental). With no signal the noise goes down the -101dBu. Perhaps the spurs are a hardware processing artefact or due to jitter? I notice spectral peaks centered around 48kHz so perhaps the internal sample rate of the DDJ-400 is related to 48KHz and we are seeing clocking errors or resampling?

1640880445649.png

The spurs are also present when FOOBAR200 is used for playback and so are not a Rekordbox playback issue.

Effect of output level control:​

Master Level PositionOuptut [mV]Output [dBu]
0dB (max output)753-0.25
End of white section751-0.27
Halfway white section504-3.73
Start of white section332-7.36
Dot 6210-11.3
Dot 5 (midpoint)101-17.7
Dot 446.1-24.5
Dot 316.2-33.6
Dot 24.02-45.7
Dot 11.09-57.0

For 9dB of headroom with 1Vrms max input devices like 3E audio DSP output level control should be set to start of white section (-7.36dBu)

For 9dB headroom with 2Vrms max input devices (consumer line level) output level should be set to max output (~8.5dB headroom) or mid white section (11dB headroom).

For devices that can accept high amplitude signals (mixing desk, audio interface etc.) the Master output should be set to maximum to optimise SNR.

Channel level red lights will engage the Rekordbox limiter even if the Master level control is below maximum as the Master level control just scales the DAC input data in this controller and the Rekordbox software has no knowledge of its setting. Therefore even if there is DAC headroom available too high channel level will cause the Rekordbox limiter to engage.

Frequency response:​

Frequency response measured using full range pink noise. Trim set midpoint, level set to maximum, 9dB mixer headroom. No differences noted at lower master out level than maximum.
1640880678366.png


Occasionally anomalous frequency response appears from DECK 1 on left and right channel. Not observed on DECK 2 and intermittent on DECK 1. Appears to be processing bug in Rekordbox? Using FOOBAR2000 to output the pink noise shows higher level but no anomalous behaviour.

Filters NXS2 ISOLATOR mode:​

1640880706231.png


Conclusions:​

The hardware potentially looks to have good enough performance (around CD quality) but there is some very odd behaviour such as the DECK1 frequency response issue and the spurs on the 1kHz test tone that suggest Firmware/Software issues. As my unit has SPDIF capability I will conduct some of the tests using digital output when I have SPDIF input hardware. I am also keen to test another unit that isn't modified.
 

AnalogSteph

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Perhaps the spurs are a hardware processing artefact or due to jitter?
Looks like jitter... ~90 Hz is an odd frequency, USB packet noise perhaps? I'm also fairly convinced that sidebands -70 dB down at 1 kHz would equate to a crapton of jitter. In a device like this I would be looking at speed / pitch related features as a potential culprit.

I notice spectral peaks centered around 48kHz so perhaps the internal sample rate of the DDJ-400 is related to 48KHz and we are seeing clocking errors or resampling?
Much simpler, these are clearly the images of your 1 kHz test tone after going through reconstruction + analog filtering. (Not sure what is being used as a DAC, but around -70 dB would match the filter performance of a CS4344 or similar.) Yes, clearly 48 kHz at work there.
 
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kipman725

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The side bands I don't think where caused by speed change features as they where also present when I used foobar2000 for playback. The speed changing is performed in software by Rekordbox and not on the controller.

I'm not sure if this is a useful test in this circumstance but I played back the REW J-TEST signal at 24bit (Rekordbox):
1641083574214.png


and 16bit (Rekordbox):
1641083488864.png


I also tried loading ASIO4ALL and using foobar2000 for playback of the 24bit signal:
1641084795255.png


Limited to two averages as REW has a bug only saving 60s long files.
 
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kipman725

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As a sanity check I re-ran the 1kHz test tone with ASIO4ALL and Foobar, the sidebands disapeared! (24bit WAV):
1641085185265.png


and without ASIO4 all:
1641085349129.png
 
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