Sony RSX-GS9

It is clear that increasingly the design motivation for motor vehicle head units has been to provide devices that do all things for all people. Music, yes! Of course! But video too, both for entertainment and practical purposes (eg. for use with a reversing camera). Navigation to get you where you want to go, and hands-free telephone calls.

Sony, of course, does that with the best of them. However with the RSX-GS9 it has gone back to the roots of car stereo, delivering a device designed only for pure, high fidelity audio.

Hi, high-res
Actually, not just high fidelity, but high resolution. That is, this unit supports such formats as ALAC (Apple Lossless) and FLAC, plus uncompressed (Mac friendly) AIFF and (Windows friendly) WAV. It can handle resolutions up to 24-bits and 192kHz. Plus Sony’s own Direct Stream Digital format. It can play the standard version of this, with 2.8MHz sampling from USB, and both that and the double rate 5.6MHz version when in USB DAC mode. Of course it also plays MP3, WMA and AAC, so your not-so-high resolution audio is fully covered. USB DAC? Yes indeed. We will return to that.

Why high res? Will you get any real advantage out of that in a car? Likely, but if you want to, you’ll need to get some high resolution super tweeters. And indeed a suitable amp, because the RSX-GS9 really is a source device and sound processor only, not an amplifier. Sony provided the high powered XM-GS4 four channel bridgeable power amplifier ($499) and a pair of XS-GS1 super tweeters ($399) – capable of delivering over 40,000 Hertz – to assist with the review. But even if one doubts the sonic advantages, it’s damned convenient because it means that you can play the exact same files that you have in your high-fidelity system at home in your car, without having to convert to MP3. But let’s get into the details.

Sony RSX-GS9The RSX-GS9 is a standard DIN-sized head unit (sans amps, as mentioned). But it looks nothing like any head unit you’ve (or we’ve) seen. Instead, once installed it looks like a very classy piece of high fidelity equipment. To the left there’s a simple, single-line alphanumeric display with four small keys underneath. To the right is a 3.5mm auxiliary input, a USB socket and a Micro-B USB socket. In the middle is a large rotary volume control knob with a nicely-lit ring around its base. There are further inputs around the back: another USB (supplied with extension lead) and on the main loom two speaker level inputs for feeding in the output of an existing car stereo. There’s also Bluetooth support, for audio playback, for control and for hands-free phone operation. For the latter purpose a microphone is supplied.

For Bluetooth music playback the standard SBC codec is supported, along with AAC (good news for those who use Apple devices) and LDAC, Sony’s own high bitrate codec. That last should make for improved Bluetooth sound for those with compatible Sony Android phones. Those Android phones supporting AptX – such as my own Samsung Galaxy S6 – will have to make do with the lesser SBC codec. Or connect using the Micro-B USB socket. It is this which provides access to the USB DAC function. You can, in fact, use this with a Mac or Windows computer, but its main use is with Android phones.

The two regular USB sockets support a direct digital feed from iPods and iOS devices in addition to flash memory. The Micro-B USB socket supports a direct digital feed from Android phones. But only Android phones that support On-The-Go (OTG) connections. If you’re unlikely to change phones soon and you’re uncertain, I’d suggest checking compatibility at your local Sony car audio retailer.

Finally, the unit has an FM tuner, but not AM nor DAB+, so your broadcast listening options are limited unless you leave your old car stereo installed, running through this unit’s auxiliary input.

Sony RSX-GS9Details, yet more details
The Sony RSX-GS9 is not just a source device, though. It’s a proper car audio front end, needing only plain power amps to complete it. So it has six RCA outputs: two front, two rear and two subwoofer. There is a full set of setup features, such as a 10-band graphic equaliser (with a bunch of presets in addition to your own custom settings); such as a low-pass filter for the subwoofer outputs (which can be set to mono) with eight frequencies from 50 to 250Hz and an adjustable filter slope (12 to 48dB per octave); such as a high-pass filter for the main speakers with similar settings; and such as a time alignment facility. There’s enough there to thoroughly tune the sound for your position in your car. Except, perhaps, for when you’re listening to DSD music. This lacks the full setup for the subwoofer, providing only the option of adding a 150Hz low-pass filter for the subwoofer output.

Now this makes sense. Direct Stream Digital is not an easy format to process digitally. Indeed, studios which use it convert to an extremely high resolution PCM format – DXD – if they do need to do any digital processing, and then convert back afterwards. So the range of digital filters offered for the PCM-based formats (FLAC, ALAC, MP3, etc) can’t be applied to DSD if it is kept ‘pure’ (ie. not converted to PCM). That means that a simple analogue crossover filter is the only option. But what was puzzling was that when I was playing DSD music from USB, it was clear that all the digital processing was working just fine. I could adjust the EQ, or change the time alignment, and the sound would change accordingly. A close examination of the manual revealed what was going on. If you feed in DSD by means of USB storage into one of the standard USB inputs, then it is actually converted to PCM (probably with 176.4kHz sampling), so all the usual processing can be applied. However, if you feed in the DSD via the Micro-B USB socket (ie. the USB DAC input), then it is kept in pure DSD format up until it is converted to analogue.

So for pure DSD you will need a Mac or Windows computer or an Android phone which is capable of providing audio over an OTG connection. With all three you will also require player software capable of delivering DSD over PCM (DoP) in which the DSD is disguised to look like PCM, but which is recognised appropriately by the DAC. I used USB Audio Player Pro software on both the phone and a tablet. This sidesteps Android’s normal functions to deliver digital audio in the original format, or DoP for DSD.

Interestingly, the Samsung Galaxy S6 phone could also deliver full 24-bit, 192kHz PCM even using its standard music player. Incidentally, you can use the ‘display’ key on the small remote control to cycle through display modes, one of which shows the input audio format so that you know exactly what you’re getting.

Making all the settings could be a slow and tedious process when working via a one line text display. The easier thing to do was to install Sony’s SongPal app on my phone. That done, once connected via Bluetooth (a simple NFC tap on the unit’s volume control did the trick) the app started up and allowed me to select inputs and, more importantly, adjust all the unit’s settings via a graphical interface. This proved to be far more convenient. The app is available for both Android and iOS.

Sony RSX-GS9

I listened to a lot of music using the Sony RSX-GS9. Some radio, but mostly a mixture of MP3 and AAC content via Bluetooth from my phone and an iPad, and even more uncompressed and high resolution audio from USB flash memory and phone. And I must say, if there’s a difference between a high-end, high-fidelity, high resolution, home audio player and the Sony RSX-GS9, it was far from obvious. I know because I did a lot of listening using the system as a source for my high fidelity system. Smooth sound, superb imaging, utter digital silence where appropriate: the RSX-GS9 simply delivered the sound as held in the files with total transparency. I loved it.

Just as importantly, it must be mentioned how smoothly it all went. The unit played all the audio without a single hiccups, even the 5.6MHz DSD in DoP format from the phone (the unit correctly reported the sampling frequency). That’s a lot of data being fed in, and it just plain worked.

Sony RSX-GS9But there was one more thing I figured ought to be done. Look, you can’t toss out words like ‘High Resolution’ without expecting those of us possessed of a sceptical temperament to check things out. Many people seem to believe that they can pick by ear whether a signal is high resolution or not. I don’t have that much confidence in myself. So I measured it. There’s good reason to. Let’s assume that the unit is perfectly designed and can deliver true high resolution audio from USB media. Well, how about from a phone? Even using an OTG connection, the phone hardware itself could act as a digital bottleneck, limiting the output to mere standard resolution. So I checked the performance of the unit using a 24-bit, 192kHz test signal, fed both from USB and from the Samsung Galaxy S6 via an OTG connection. The news was nothing but good. Extremely good in fact.

The performance was identical to two decimal points either way. The frequency response extended all the way out beyond 56kHz at -3dB and 70kHz at -6dB. That’s the kind of performance you expect from a high-end, high performance home DAC. The noise performance was very nearly as good: -107.6dB A-weighted. This unit adds absolutely no audible noise to the signal. The total harmonic distortion measured at an insignificant 0.0013%. The intermodulation distortion at 0.0032%. If you’re not an avid high-fidelity magazine reader and these figures mean nothing to you, just be assured that if they were to somehow be improved upon, no-one on the face of the earth could tell the difference.

As for DSD, the performance was pretty much the same. The noise floor was just one decibel higher. The -3dB frequency response point was at 50kHz in accordance with the recommended anti-aliasing specifications for DSD, and -6dB was at 62kHz. High resolution PCM or DSD, you’re going to get the same effective performance, barring only the differences in signal processing, and then only if you’re keeping your DSD pure.

Do note: the phone measurements will only reach this high standard if your Android phone delivers the sound in full. It is almost impossible to be certain without testing the phone, or finding a reputable publication that has tested it.

Clearly the Sony RSX-GS9 is not the head unit for everyone. But for those who want the highest quality music available in a vehicle, it must be sitting at the top of the ‘want’ list!.

Sony RSX-GS9

Sony RSX-GS9 Digital media player
Price: $1999

+ Superb audio performance, High resolution audio, Smooth, trouble-free operation
-  No AM or DAB+... but it’s about quality audio

Type: Head unit pre-amp with high resolution DAC

Features: Text display, Bluetooth (hands-free/music streaming; mic supplied; SBC/AAC/LDAC codecs), front panel USB, USB-DAC/OTG function, supports MP3, WMA, WAV, AIFF, AAC, FLAC, ALAC, DSD (DSD at 2.8MHz, 5.6MHz via USB-DAC function; PCM to 24 bit, 192kHz)

Product page: Sony Australia