What exactly is the purpose of a transport? I see these as boards for the RPI but I’m not clear about their purpose. Any help is appreciated.
—still learning this great hobby…
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Short Answer
- Transport: stores or wirelessly streams digital audio data
- DAC: Digital to Analog Converter, converts digital audio data into an analog signal
- Amplifier: Amplifies an analog signal to a level where it’s powerful enough to drive a transducer
- Transducer: A device like a headphone or speaker that converts an electrical signal into sound waves which we can hear
Long Answer
The purpose of a “transport” is to transport audio data from one place to another. Sometimes you’ll see the term used to refer to something like a digital audio player or phone that physically contains the music (or can access streaming services like Spotify directly). Sometimes you’ll see it used to describe something like a Raspberry Pi or Chromecast that can be used as an endpoint for casting audio from a centralized server like with Roon. It can also be used to refer to something that can read data from audio CD’s and send the data out via a digital audio interconnect like S/PDIF. Cambridge Audio has a great explanation of how a CD transport differs from a CD Player.
The important distinction between a “transport” and a “DAC” is that a transport is simply responsible for transporting digital data, whereas a DAC (Digital to Analog Converter) converts that digital data into an analog signal that can then be fed to an amplifier from which it can drive a transducer like headphones or speakers. In practice, the thing that handles transport duties often also includes a DAC and sometimes even an amp. So for example my phone serves as a portable audio transport and has a DAC (and amp) so that it can directly drive my headphones. I’ve also got a Raspberry Pi with a Hifiberry DAC which handles transport plus DAC duties, but feeds an Ember II which handles the amplification work. This is similar to a Chromecast which you would hook up to an amplifier as well. Lastly, I’ve got a Raspberry Pi that simply handles transport duties and connects to a Topping NX4 via USB, with the NX4 doing DAC + amplification.
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A good question. Years ago, the stereo system was a lot easier to understand. I first heard the term “transport” in reference to the disc spinning part of a CD player with an outboard DAC. The first CD players (and most of them still today) had the DAC built-in, but the folks at PS Audio, Theta, Wadia, and others discovered some advantages to moving the digital to analog conversion circuitry into a separate chassis with its own power supply and vibration isolation. Not long after, a few companies started making dedicated CD transports with no built-in DAC.
For most of us, the CD transport has been replaced by a computer of some kind. The S/PDIF connection that was popular between CD transports and 1st generation outboard DACs has largely been replaced by USB.
The “amp” is probably the easiest bit to understand since its purpose has not changed. It sits between passive loudspeakers or headphones and the analog output of the DAC…along with an attenuator to adjust playback levels.
In this world of headphone playback, a popular component is the DAC/Amp which is really just a DAC and headphone amp that are stuffed into the same chassis. Of course, a DAC/Amp can’t do anything by itself…it needs a digital source. This could be a computer, tablet, smartphone, streamer/renderer, etc. Harkening back to the compact disc days, these things are sometimes collectively referred to as transports.
Hope this helps!
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So, and I remember this question from my old stereo days, is it better to separate those pieces out into separate circuits. A RPI transport board connected to a separate DAC connected to a separate amp, or an all in one headphone amp board that handles the DAC and the small amplification jobs, or some other combo?
I’m sure opinions abound, just like in the room stereo world. J
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The practical answers is “it depends”.
There are as many technical/engineering benefits to separating functions into discrete “boxes” as there are drawbacks. For example, using a pure transport and feeding a pure DAC means that, typically, while you’ve isolated the PSUs and other sensitive electronics from each other, you’ve made your clock and data transmission much more susceptible to issues.
In general, all-in-one units tend to give you less room to get the absolute best performance for any given aspect of the overall replay chain. You won’t often find the very best DAC coupled with the best amplifier simply because it’s rare for the best DACs to come from companies that also make the best amplifiers.
At the same time, an AIO can be very specifically matched, internally, so that the components have good synergy/complimentary specs, and some of the additional complexity and interfacing required for separates can be avoided (at least in the view of the designer/engineer).
For me, personally, I like AIO solutions for convenience and cost-effectiveness, but for critical listening I tend towards completely separate components so I can pick what I like the best in each role. Sadly Woo Audio and Chord do not offer an M-Scaler equipped DAVE with a built-in WA234 output!
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Yes. My everyday system is intentionally easy to use, and I have little need for optimal separates. My musical tastes run all over the map, and I’d much rather spend my time finding and listening to new music. The source/masters are often mediocre on a technical level and will never be great.
Regarding cost-effectiveness, you get far more for your money today than a generation or two ago (inflation adjusted). The functional quality gap is closing. At the same time, the equipment-as-art and snake-oil salespeople will sell you a fancy functional sculpture or the emporer’s new clothes any day of the week.
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I would just add that technology changes faster for some types of components than it does for others. A reference grade headphone amp from ten years ago is very likely to compare favorably to current models…and that will probably still be true ten years from now as long as it is well cared for.
The same does not apply to DACs since the technology changes more rapidly. I tell people to think of a DAC like they would a laptop or (if you are into photography) a digital SLR camera body. Even a top quality DAC from five years ago will be significantly behind current models in resolving power, supported formats and features. You would not buy a five year old laptop for critical work…so don’t buy a five year old DAC for critical listening…or expect the DAC that you are using today to still be cutting edge a few years from now.
Transports are no better than DACs (possibly worse) since many are nothing more than small board computers these days. Even the so called bridge cards that you can add to certain DACs to make them “network enabled” are actually just a small Linux computer (or similar) running on a card.
When you’re optimizing for performance + quality per dollar spent over a given period of time, it makes sense to invest more heavily in the components that are likely to give you the longest runtime: headphones and amps. Spend less of your budget on components that will become obsolete more quickly: DACs and transports.
With the all-in-one route, lifespan of the entire unit is limited to the shortest lifespan among all internal parts. Upgrading the DAC might mean discarding perfectly good amp circuitry, for example.
An inexpensive all-in-one system is fine for getting started–knowing that you’ll eventually sell it or give it away…but I personally would not spend thousands of dollars on one.
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A transport’s only function is to read the digital signal and though several interfaces send the information to a DAC(digital to analog converter) that converts the signal to an line level analog signal that a pre-amp or receiver, which can then send it, through a volume control, to a power amp that drives a pair of speakers or headphones. Separate tansports and DAC’S are rare and very expensive.
There are myriad transports available starting at $35 or so.
Dedicated DACs start as low as $20.
And that’s if we stick to things from companies people have very likely heard of. So not really rare and definitely not expensive.
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