The last few weeks I have been recording using the Yamaha SW1000XG together with a Joemeek VC3 preamp/compressor. During some recent sessions I had problems keeping the bass distortion‑free. I got a great input from the VC3 into the SW1000XG but the bass was distorting on the output, even though the recorded WAV file wasn't peaking at 0dBFS.
While mixing some of the tracks, I felt that the sound was distorted in some way. I started checking some things with reference CDs and then the real problem began to show: the SW1000XG's outputs were distorting!
I played my reference CD via my Technics SLP212A, Rotel hi‑fi amp and Beyer headphones. Everything sounded fat but nice and transparent. However, when I played back the same track through the SW1000XG I could hear some distortion in the low end and the transparency was somewhat gone, as were the highs. I used XGedit to check if there was an EQ in the output signal and I also tried lowering the output level really low. Nothing got rid of the distortion and I concluded that the distortion was not because of an impedance problem, because even at a very low level it sounded distorted. I think that the main EQ on the SW1000XG's output is the troublemaker. You can't bypass the thing and you can only put the controls to zero. You have to have great ears to hear all this! The distortion is rather small, but it's there and it's driving me crazy.
Marco Raaphorst
Martin Walker replies: If you're getting distortion this could be due to the fact that the SW1000XG Input Gain defaults to Mic level. You can change this to Line level using an editor like XGedit95 or XGWizard, but if you download the latest firmware upgrade from Yamaha's web site (www.xgfactory.com) this will change the default setting to Line as well as improve various other aspects of performance. The audio channels also default to central Pan positions, so you will need to pan them full left and right respectively when auditioning stereo tracks.
These two points have caught a lot of people out, but somehow I don't think they totally answer your query. Like you, I've got an SW1000XG, and have noticed that its frequency response doesn't sound flat, but is instead distinctly warm at the bass end. I called Yamaha UK and they confirmed our suspicions that the problem is caused by the five‑band EQ that forms the final part of the SW1000XG audio chain. This has five settings labelled Flat, Jazz, Pop, Rock, and Classic, and these all mess about with the frequency response in various ways, unfortunately including the Flat one.
I measured the output frequency response of the SW1000XG using Cubase, a special test signal containing equal level sine wave tones every 1/3 octave, and Nick Whitehurst's FFT Spectrum Analyser plug‑in, and this confirmed that it shelves upwards by several dBs below about 500Hz, which accounts for the warm sound. After spending some time experimenting with the five‑band EQ I've come up with a set of values that get its output frequency response as flat as possible. Here are the changes you'll need to make. First select the Flat setting. Band One at 80Hz and Band Five at 8kHz should both be left at 0dB, but Band Two at 500Hz should be increased to +1dB, Band Three at 1kHz to +1dB, and Band Four at 4kHz to +2dB.
Don't worry about the fact that these are above 0dB — this shouldn't cause any distortion since Yamaha's design apparently reduces the level of the digital signals by 6dB before reaching the output effects and EQ to give them some headroom. If you're using a utility like XGedit95, the easiest thing to do is to save these settings (along with the input gain set to Line level) as a file named Default.xge, and then load this is as a template whenever you start a new song.
Since these five‑band EQ presets are burnt into one of the Yamaha custom chips (the SWP30) you will find my tweaked settings also work for the MU100, MU128, and probably other models with a similar EQ section. Try it and see if it makes your sounds seem flatter!