In this age of major technological advances, the different audio formats can be confusing. A great example is PCM audio and FLAC, covered here today.
PCM (Pulse Code Modulation) is a standard sampling algorithm used in analog to digital conversion (ADC). FLAC, on the other hand, is a lossless container format that compresses audio files to use 40-50% less storage.
Uncompressed and original audio recordings can be stored using PCM Audio that can be converted to and from lossless FLAC, bit-perfectly.
Can you hear the differences between the two? Let’s look at what each format entails first.
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PCM audio explained
PCM standing or Pulse Code Modulation is a digital sampling method where bits (0s, 1s) are sampled and represented from an analog signal. These samples are taken at regular intervals at sample rates above 40kHz (40k samples per second).
The sample rate should be 40kHz or above because of the Shannon sampling theorem (Nyquist theorem). It states that for the most accurate representation of an analog signal from a digital one, the sample rate needs to be at least twice the highest frequency.
And because the upper limit of human hearing is 20 kHz, the ideal minimum sample rate is 40 kHz. Higher sample rates are used (oversampling) to account for any imperfections hence sample rates of 44.1 kHz, 96 kHz, and so on with 44.1kHz being the standard. The way they arrive at these sample rates is a story for another day.
A sample rate of 44.1 kHz will mean that the audio recording will have a maximum frequency of 22 kHz. What’s more, a higher sampling rate will mean that more storage is required for the audio file.
In summary, a higher sampling rate means that more high-frequency audio information is available for playback.
Apart from the sample rate, the bit depth is also crucial in PCM.
Audio bit depth (number of bits per sample) determines the dynamic range for particular soundtracks and is denoted in dB or decibel. Dynamic range is essentially the difference between the highest (loudest) and lowest (quietest) amplitudes of an audio signal.
The common bit-depths are 8-bit, 16-bit, 24-bit, and 32-bit with 16-bit being the standard. Every bit is equal to a dynamic range of around 6 decibels (. So, with a bit depth of 8 bits, you would have a dynamic range of 48 dB, 96 dB for 16 bits, and 144 dB for 24 bits.
The relationship between decibel levels and perceived loudness is complex. But what you need to know is that the decibel level, where bit depth is concerned in PCM audio, is a measure of the electrical content in an audio file or the audio file’s resolution.
According to psychoacoustics (study of how we perceive sound), the maximum dynamic range for us is around 120 dB with our threshold of hearing being around 90 dB.
144 dB is within the threshold of pain and would be impractical for anyone while 48 dB is too low. This leaves us with a 96 dB sweet spot or a bit depth of 16. A bit-depth of 16-bits is all we would need for rich audio playback but is often exceeded.
During mixing, a bit depth of 24 may be preferred by some as it makes dealing with room noise easier and also increases the buffer before which clipping can occur as the noise floor is lowered. The noise floor drops with an increase in dynamic range and the fewer the bit the more noise you get (less headroom).
Sample rate and bit-depth knowledge are crucial in understanding PCM.
FLAC audio explained
FLAC (Free Loss Audio Codec) is a lossless container format and is essentially a set of algorithms that determines how digital audio can be compressed for the most accurate representation.
When FLAC compression is used, the uncompressed file and lossless FLAC will be similar to each other bit for bit. FLAC files can, therefore, be uncompressed and reversed to their original format during decoding.
For example, after ripping (copying) a PCM file (CD quality) to FLAC for storage in your home media server, you can easily convert the file back to PCM if need be.
The advantage that FLAC has over uncompressed audio, PCM audio files included, is that it uses significantly less storage. This is usually about 40% less storage.
The way FLAC accomplishes this lossless compression is by removing redundancies (useless parts).
Files are also compressed through other smart means such as rearranging bit strings. Take this sequence for example: ABCDABCDABCDABCD. What FLAC would do on encountering something similar is rearranging the sequence to (ABCD)4. This would effectively compress the sequence but can be uncompressed to its original form.
This is an oversimplification, but you get the gist. The same thing happens during FLAC compression but in bit sequences instead of letters.
Also, in most cases, this lossless format will have a similar sample rate and bit depth as the uncompressed file. But keep in mind the standard which is 16 bit/44.1kHz.
Which sounds better: PCM audio or FLAC
This is a huge point of contention for a considerable number of audio enthusiasts. So, I am going to try and demystify it in the simplest terms possible.
There are no sound quality differences between PCM and FLAC files as long as the conversion goes right which it most probably will. This is because as we have seen, FLAC is a bit-perfect compression of the original uncompressed file, PCM in this case.
If you reconstruct a PCM file from a FLAC file, you are going to get something similar. Although FLAC is not entirely lossless (no compression format is), any lost details will not matter since they would be out of our audible range and we can, therefore, not hear them (no one can).
Remember when I mentioned that there is an upper limit to how much we can hear as far as frequencies and dynamic range are concerned. Yes, anything above those values (16 bits and 44.1 kHz due to oversampling) does not matter as much.
What’s more, there will be no sound quality difference between a 16bit/44.1 kHz FLAC file and a 24bit/192 kHz PCM file, NONE.
If you still believe that you can hear a difference between PCM audio and FLAC, I would like you to attempt this challenge. Take two identical files (same artist, same song, and so on), one PCM, and one FLAC.
On your computer, install Audacity, open it and open the PCM file using it. Open the FLAC file on the same timeline but this time invert it, then render the difference. What you will be left with is digital noise which is essentially silent and will have nothing to do with what you hear upon playback.
So, before you decide to convert your FLAC collection to PCM, these are important considerations.
FLAC vs PCM: Comparison table
|Is an uncompressed format||Is a compressed but lossless format|
|Offers high-quality audio playback||Offers high-quality audio playback|
|Is used to archive original recordings||Can be used to archive PCM files|
|Requires more storage and bandwidth due to the larger files||Takes up less storage and takes up less bandwidth due to the smaller sizes|