It's commonly claimed that records have a "warmer" sound, especially when sourced directly from an analog master, compared to CDs, which are 16-bit 44.1 Khz pulse-code-modulation files. Vinyl records store sound as analog grooves, which are often claimed to be exact replicas (analogues) of the original sound waves. We will see that this is not quite true.
When it comes to a digital format such as CD, the original sound waves are quantized into discrete points, shown below.
This process is called sampling. The dots represent coordinate points on an x-y axis that the sound wave originally passed through. When a digital file is played back, it is processed through a digital-to-analog converter (DAC), which "connects the dots" and re-creates the analog file. In reality, there are far more coordinates than in this illustration. CDs are 16-bit, 44.1 Khz files, as mentioned before. What this means is that for 16 bit audio, there are 65,536 levels of the y axis on which a sample can lie. 44.1 Khz refers to the fact that 44,100 samples are taken each second, 22,050 in each stereo channel. This refers to how many samples are actually used out of the bit depth. 16-bit audio provides 65,536 possible levels, and a sampling rate of 44.1 Khz per second uses 22,050 of those possible levels in each stereo channel. The number of available levels double with every bit. In practice, there are 16-bit 44.1 Kz, 16-bit 48 Khz, and 24-bit files ranging from 44.1 to 88.2, up to 96 Khz and 192 Khz sampling rates. Essentially, increasing the bit-depth and sampling rate is like increasing the megapixels in a camera. It gives more pixels (samples) from which a picture (sound wave) can be reconstructed. To use the connect the dots metaphor, this gives the DAC more dots to work with to reconstruct the original sound wave. The problem is that DACs vary wildly in quality. Some cheaper ones are the equivalent of getting a drunk to play connect the dots, and result in very poor sound, while better DACs are more of a master artist carefully connecting the dots. Even after the dots are connected, the jagged waveform must be smoothed out.This is done by a process called interpolation. Depending on how well the DAC performs interpolation, it may introduce digital distortions that are quite unpleasant.
This is where sampling rates above 44.1 Khz might be useful, although there is debate over whether or not you can hear results. It is difficult to tell in practice if 48/88.2/96/192 Khz sampling rates are really better since playback equipment varies wildly. Double blind studies suggest that the differences are inaudible to most people.
When it comes to Mp3s, Mp4, WMA, and AAC files, these are called "lossy" files. They take the original digital file, called a lossless file, discussed above, and degrade it even more for the sake of hard drive space. They do this in various ways, but all involve cutting down the number of samples. When a file is played back, the samples are played back at a certain rate, define by the number of bits played back per second. A CD file has a sample rate of 1411.2 kilobits per second. That means that every second, 1,411,200 bits per second are available to be played back. To see how this is calculated, we take 44.1 (the sample rate) and multiply it by double the bit depth, which is 16. Hence, 44.1 times 32 = 1411.2. This is lossless, since during the bits played back per second, nothing is lost. However, lossy formats use various algorithms to select sound frequencies relatively less audible, or even inaudible to human ears, and deletes them. A 320 Kbps Mp3 file has 1/4.41 the data of the original lossless file! A one minute file at 16-bit 44.1 Khz audio with a lossless 1411.2 kbps bit rate will have a file size of 10.1 MB. A one minute file 16-bit 44.1 Khz at a 320 Kbps bit rate will be 2.29 MB in size. Keep in mind, 320 Kbps is the maximum bit rate across the lossy formats. 320 Kbps is usually very close to CD quality once played back to most people and on average equipment, though more intangible details such as stereo separation or immediacy seem to suffer when played back on higher quality equipment. Lower bit rates start to chop off frequencies more audible to the human ear and sound far inferior to the original file on even average playback equipment.
So, in summary, digital files can be either lossless or lossy, and exist as samples of the original sound (x-y coordinates, where y is the time variable), and are are played back by a digital-analog converter, which connects the dots, then smooths them out. Vinyl records work entirely differently.
Records contain grooves, which correspond roughly to the original sound wave. However, it is NOT an exact replica of the original sound wave. If the original sound wave were etched into the vinyl, it would be unplayable because the stylus would bounce around so much that it would jump out of the groove. The reason for this is that low frequencies cause bigger stylus vibrations. So, to compensate, a standardized equalization is applied. Bass frequencies are greatly reduced in volume, while high frequencies are greatly boosted. This allows a groove to be etched that only minimally causes the stylus to bounce back and forth in the groove. Of course, this bouncing is what produces the sound, but if it gets to the point where it bounces out of the groove it doesn't do much good! Then, once the record is played back, the resulting RIAA-equalized wave is un-equalized by boosting the bass greatly and reducing the treble in an exact inverse of the original equalization.
The result is something very near the original sound wave. In reality, perfect restoration of the original wave is impossible as the circular nature of the record causes some distortion. Just as the playback of a digital file depends on a quality DAC, the proper playback of a record depends on a proper pre-amp to unequalize the sound. Quality record playback also depends on a quality stylus and cartridge to pick up the sound to begin with. The better the pickup mechanisms, the less distortion there will be to the sound and the closer the sound wave will be to the original master once played back. Perfection is impossible, unless you have a laser pickup instead of a stylus and cartridge. This raises a very important point. Playing your records on a badly calibrated turntable or on a cheaply built Crosley, Jensen, or some other big-box-retailer brand will damage your records and produce inferior, distorted sound. They have been measured at tracking the records with anywhere from 5 to 12 grams of force, which scrapes away at the grooves with every playback (they also often spin at the wrong speed, often a bit too fast). A quality turntable will have a tracking weight adjustment to adjust to the specifications of your cartridge, as well as an anti-skate control to minimize groove distortion from the record's circular shape. A good cartridge should track from 1.5 to 3 or 4 grams. Stay as close to 2 grams as possible. Getting quality record playback is a lot more expensive than getting quality CD or Mp3/Mp4/AAC/WMA playback. For this reason, digital formats may be preferable to you.
So, both digital and vinyl records follow the same pattern. Both are altered forms of the original sound wave, digital being sampled, and records being RIAA-equalized. Both must have the original sound wave restored, by a DAC for a digital file, and by a pre-amp for a record. So long as the equipment used to play them back is good quality, distortion should be minimized, and similar results obtained. However, this whole time, I have been assuming that the sound waves are identical going into the record and CD. In reality, CDs and records often receive different masters. Some record releases have an entirely special master done, either at the time of release or later on when an older album is re-issued. The differences can be subtle, but most often, the record has more dynamic range. Due to a phenomenon called the loudness war, since the late 1990s CDs have been mastered to have all sounds play back at rougly the same volume. This is done to enhance the perceived loudness of the recording. However, the music loses its life when this happens. When everything is played back at the same volume, there is no "room to breathe" between instruments. Everything sounds like a "wall of noise." Even older recordings before the loudness war often suffer when they have a new re-master done for CD release. Below is a comparison of the waveform for the 2011 remaster of Nirvana's "Smells Like Teen Spirit" compared to the Mobile Fidelity Sound Labs remaster. The 2011 remaster has a lot of digital distortion, marked with red by Audacity. The Mobile Fidelity release, mastered at a much lower volume with more dynamic range, lacks the distortion.
While at first listen, the louder master may sound more attention grabbing and "better", the lack of dynamic range makes the music have less of a "live" sound. Listening to entire albums mastered this way may cause the music to become boring. Perhaps this is part of why many now have "song ADD" and skip tracks a lot, since nearly all music is mastered like this or worse. Once the lower volume, more dynamic, recording is turned up to a louder volume, the separation between instruments is more apparent and instruments like the drum have a stronger impact. Take for example the below comparison of the Guitar Hero version of a Metallica song, which has dynamic range, to the completely brickwalled CD version.
Notice how the CD version's drums have no impact at all! The problem with everything being the same volume or close to the same volume in a recording with a lot of dynamic range compression applied is that relative impact of instruments is lost, and when the music is turned down, everything loses impact. When turning it up, nothing gains any impact, but instead the digital distortion becomes very obvious.
As mentioned before, when bass is too loud, the record stylus is likely to jump. Even with RIAA equalization, if the bass-frequencies are super loud because of dynamic range compression, the stylus risks jumping out of the groove. For this reason, a master with better dynamic range (and hence, likely less jacked-up volume on bass frequencies) is used. In some cases, it is still a 16-bit 44.1 Khz CD quality file passed through a studio quality DAC then cut to vinyl, but the better dynamic range will still make it sound better over the CD master that has dynamic range compression over-applied. Most often though if a vinyl record is made from a digital master, a 24-bit 96 Khz or 24-bit 192 Khz file is fed through the DAC before cutting to vinyl. This makes for a more accurate groove on the record. A 24-bit sourced vinyl with plenty of dynamic range can sound as good as an old fashioned analog-recorded, analog-mixed and mastered, record. In theory, CD is capable of far more dynamic range than vinyl, but in practice, vinyl often comes out ahead. This is why vinyl often sounds better than CD/digital. CD is capable of sounding just as good, if not better. Records introduce pops and clicks from dust caught in the grooves, and due to the sensitivity of the playback equipment involved, quality varies wildly on how they sound. However, vinyl records offer something tangible CDs don't. They have bigger artwork, bigger lyric sheets (when included). Digital files on a hard drive lack any of this at all. Because of the loudness war and the tangible properties of owning a record, many prefer vinyl as a format, including the author. Others may prefer the smaller storage space of CDs, or the consistent pop-and-crackle free sound CDs have. Others may prefer the convenience of a digital file on a hard drive. With this information, you can choose which music format you prefer.
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