Some Technical Notes on DAC/amps
This contains information relevant to a companion piece reviewing DAC/amps.
The difference a DAC/amp makes
The conversion from digital data to analog signals is typically completed by a microchip. The better the chip, the higher the quality of digital files they can handle. These microchips are now relatively inexpensive and plentiful, and in a year or two they will all probably be able to handle every kind of digital format, so the chip itself, already less important, will become even less significant in the future.
However, what will continue to be important is how the microchip is integrated with other components. A poor integration can introduce subtle bits of noise or distortion which can interfere with sound quality. Therefore, even though the on-paper specs can look the same across DACs, the output can be different.
A key spec that does actually make a difference is the output of the amp: how much power it can supply to your headphone. This is because, starting from the ‘mid-fi’ range of more expensive and higher quality headphones, more power is required to achieve the same volume. This is because of the headphones having higher impedance, measured in ohms. This, in turn, has to do with the fact that most audiophiles use pro-grade equipment, which typically puts out a lot of output, and can ‘blow out’ low impedance headphones (the physics is actually more complicated — the number of ohms is not a precise measure of what makes a headphone hard to drive — but this should suffice as a rule of thumb). There are also reports of improved sound quality with higher impedance, particularly based on the legendary Beyerdynamic DT770 Pro line of headphones, which comes at three impedance levels.
Though impedance is falling in the headphone business, your next headphone could have high impedance ratings (measured in ohms). Power-hungry headphones will require you to turn your phone volume all the way up to reach listening levels, and can make it hard to listen to quieter songs. This is why the output of an amp matters: the higher it is, the more likely it is to give you louder volumes on hard-to-drive headphones. Of course, louder is not always better; this is where the quality of the amp comes into play. Inferior amps can add noise and distortion and grain even as they increase the volume.
Another element is the audio output jack. On phones that don’t have a 3.5 mm jack, you’re restricted to cheap adapters, and on laptops and phones with audio output jacks, the quality of the jack itself can compromise sound quality. Often, computer and phone manufacturers scrimp on audio equipment because most buyers of these devices don’t really pay much attention to sound quality. A good external DAC/amp can compensate for all these oversights.
Due to the variations in manufacturing, experienced listeners widely report subtle differences across DAC/amps. In my experience, amps seem to have a significant impact on bass response, making it fuller and more impactful. A good DAC/amp also makes music sound ‘cleaner’, as if a subtle veil of noise or distortion has been removed. More subtle changes can be heard in the soundstage, as well as in how forward or laid back vocals sound.
The maximum difference in sound quality is between laptops or PCs and external DAC/amps, because there are so many more components that can add to the noise. On most Android phones, I’ve found the difference to be a bit less, but still noticeable. Of course, there are those phones that are designed to deliver high quality sound output, like the LG V series, which would make entry-level DAC/amps unnecessary. Even Apple devices do a pretty solid job at this, and entry-level DAC/amps may not offer much of a benefit. To compensate, however, the entry-level Bluetooth DAC/amps in this review add convenience, as well as a host of software features that can recommend them.
This difference also becomes more significant once one upgrades key elements of the rest of the chain. Most importantly, the more discerning and trained your ear becomes, the more DAC/amps matter. Using a DAC/amp can also help you better differentiate between lower quality and higher quality files. Higher-quality headphones will also be significantly impacted based on the DAC/amp you use to drive them.
Quick note on Bluetooth
In the past, Bluetooth data transfer was simply not fast enough to allow people to listen to high quality files. In order to still play music, files were compressed based on various Bluetooth codecs, leading to poor sound quality. There were also issues with choppy connections. Ever since Bluetooth 4.2, however, speeds have picked up, and newer codecs like Qualcomm’s AptX HD and Sony’s LDAC are capable of playing lossless audio.
There’s one other problem with Bluetooth: latency. This is the lag between when the sound plays on your computer and when you hear it over your headphone or your speakers. This doesn’t make a significant difference when you’re playing music, but if you’re watching a movie, you will see that lips move first, and the dialogue reaches your ears a split second afterwards. To overcome this, Qualcomm has a codec, AptX LL (LL stands for low latency) that allows for decent sound quality at a latency that humans can’t notice.
If one of your purposes for buying headphones and/or a Bluetooth DAC/amp is to watch movies, you need to make sure that all your devices support AptX LL.
