Streamers Have a Sound (L4)

A streamer is a device that gets digital audio streams from an online or local source and passes them on to a DAC. There are many devices that combine the streamer with a built-in DAC and then output just the analog signal for input to an amplifier or pre-amplifier. We will call these streamer-DACs. If they also have a power amplifier, then they are streamer-DAC-amplifiers or, often, integrated amplifiers.

For the most part, streamers are designed to be bit-perfect, which means that they just pass the original stream on without modifying it in any way. These streamers can’t impact the sound of the music encoded in the stream. Still, audiophiles often claim they can hear differences between streamers and even laud the sound quality enhancement of more expensive streamers.

Here are some ways this is rationalized:

• Expensive streamers use special parts that reduce noise in the streamer. Of course this doesn’t matter since the digital file is just passed on to the DAC.
• Complex streamers perform a lot of operations with their CPUs that introduces noise in the systems. Same problem, though: a digital file is not affected by any noise if it arrives bit-perfect at the DAC.
• All that noise goes out over the USB cable or other interconnect to the DAC and affects the DAC. Now we are getting somewhere. Yes, there are situations where poorly engineered DACs can be impacted by ground loops and noise over USB. This isn’t changing the digital file, however, but pollutes the reconstruction of the analog signal by the DAC. This is easily fixed by using ethernet to connect the streamer and DAC (where such is available) or using optical interconnects. There are also USB isolators available that can reduce noise carried by USB cables or you can exclusively use balanced outputs from the DAC to avoid ground loops.
• Maybe “bit perfect” is not actually true since a cable is carrying an analog signal that is tampered with by the noise and processing. This fundamentally misunderstands how digital communications work. Yes, time-varying electrical currents convey digital data but the reconstruction of the original digital data is guaranteed by checksums and other error-correcting techniques whether over TCP-IP or via USB Audio transfer to the DAC. These are highly reliable. A common thought experiment shows why: if digital communications were not reliable, banks would have errors in accounts all the time. They don’t.

For streamer-DACs or those with amplifiers it is certainly possible that processor noise damages the reproduction of the analog signal. Also watch out for streamers that apply DSP without it being easily defeatable. I personally prefer to hear a high fidelity reproduction, not one colored by the reproduction technology and that is outside of my control. In the comments by KOEN, below, my descriptions are taken to task, partially incorrectly, but it should be noted that if one is transcoding or applying DSP or room correction at the streamer, then the bits arriving at the DAC will be changed.

Here’s some great new testing of the Diretta protocol to examine whether processing in a streaming component might pollute the sound from a good-quality (but relatively inexpensive) DAC. While the work is ongoing it provides initial confirmation that there is little or nothing to be gained from special protocols for stream delivery.