Bitstream vs PCM- Which is the best decoding mode?

In a home theater, PCM and Bitstream refer to audio output settings that decide which of your devices is used to decode audio. They both offer the same quality of sound but this may also come down to the quality of the decoding device.

In Bitstream, the audio is decoded by the pre/pro, receiver, TV, or soundbar while in PCM, the source player (Blu-ray player, PS, Xbox, and so on) decodes the audio signals before transmission. If you use bitstream, the audio processor in the player is bypassed while in PCM, the audio processing on your AVR, preamp, TV, or soundbar is bypassed.

It mainly comes down to which device is better at decoding when choosing between the two. Either way, the sound signals will need to be decoded before being sent to the speakers.

If you have a high-quality preamp or AVR, you may want to take advantage of its superior audio processing. But if you do not want a performance impact on your pre/pro/AVR/TV/soundbar, you can use PCM but this will also have a performance impact on your player/source.

When it comes to PCM vs Bitstream, you can only choose better between the two if you fully understand what each output setting entails.

So, let us look at each of these options in more detail.

Bitstream vs PCM: Overview

BitstreamPCM
Decoding is done in the pro/pre/receiver/TV/soundbarAudio decoding is done at the source before transmission.
Files are encoded in bits (0s and 1s)Derives from analog signals (sine wave)
Works great with compatible devices that have the latest sound formatsWorks great with all players such as Blu-ray, DVD and CD players, Play Station, X-box, and so on.
Can be transmitted both wirelessly or through cablesRequires a cable connection between the source and the next device.
Only supports transmission of digital signalsSupports transmission of both digital and analog signals.
Can transmit surround sound for up to 5.1 channels if optical or coaxial cables are usedCan only transmit 2.1 stereo sound if coaxial or optical cables are used
Secondary audio is limitedHi-res secondary audio is retained
More flexibility is offered to the processor and speakers Requires a higher bandwidth transmission for the best quality

Similarities

  • Both Bitstream and PCM have great audio quality.
  • They can both be played in most Blu-ray and DVD players.
  • Both PCM and Bitstream will need to be converted to an analog signal before being played on your speakers.

What is audio decoding?

I keep mentioning the term audio decoding but what does it mean?

To understand what audio decoding is, you need to differentiate between encoding and decoding.

Encoding is the method by which the audio file is stored in a CD, Blu-ray, or any other media storage. Decoding, on the other hand, is the processing of the encoded audio file.

During decoding, the encoded audio file is split into various channels depending on the format before it is amplified and sent to your speakers.

What is PCM?

PCM stands for pulse-code modulation. It refers to how analog signals are digitally sampled and encoded at regular intervals in digital sound applications. PCM is mostly used in Blu-ray, DVD, and CD technologies.

To better understand this, look at a continuous analog sine wave below. For the sound to be transmitted digitally, it has to be sampled from the sound wave at regular intervals converting it to a series of 1s and 0s for manipulation and storage. This is why compact discs are much smaller than vinyl records.

The red dots represent the samples while the blue line is an analog sine wave

In the Blu-ray player or any other media player, selecting PCM reverses the bits and tries to convert them to an analog signal. For example, in a Blu-ray disk, the digital samples are converted to an analog signal depending on the discrete samples to produce a voltage that is then transmitted to the next device with no loss in quality.

The analog audio signal is then sent to the receiver, TV, preamp, and any other sound processor in your home theater, but bypassing their internal audio processing.

Transmissions can be done through digital or analog cables.

Digital cables

The most common digital cables used are HDMI cables. When using HDMI cables, you will have multichannel support of up to 7.1 channels.

However, for coaxial and optical (TOSLink or S/PDIF) cables, you will have a maximum of 2.1 channel support with PCM.

Within the digital cable, the audio is encoded and transmitted before it is then converted to an analog signal on reaching the receiver, TV, pre/pro, and so on.

Analog cables

Analog cables include RCA, XLR, and so on. The analog signal is transmitted to the receiver or any other device without further audio processing.

Depending on your port selection, you can use either of these cables.

Difference between PCM and LPCM

LPCM stands for Linear Pulse Code Modulation and is a PCM variation where the encoded samples are represented from the amplitude values on a linear scale instead of amplitude logs. With LPCM you have more sample values over a smaller set of values from the wavelength. This means that LCPM is capable of handling higher throughputs.

In most cases, PCM is used to describe LPCM. However, the 2 are different because PCM is associated with “uncompressed” stereo sound (2-ch) while LPCM is associated with “uncompressed” multichannel sound (up to 8 channels).

I am also using PCM to describe both LPCM and PCM as they are mostly similar to each other.

Pros and cons of PCM

Pros:

  • Less stress is put on your receiver, integrated, soundbar, or TV.
  • Eliminates delays or lags.
  • Better quality hi-res secondary audio (additional audio).

Cons:

  • Only supports 2 channels over coaxial or digital optical cables.
  • More strain is put on the media player.
  • The sound quality is determined by the media player.

What is bitstream?

Bitstream is also known as;

  • Audio Bitstream
  • Digital Bitstream
  • Bit Stream
  • Bitstream Audio
  • Bitstream Bypass
  • Bitstream Audiophile

In a home theater, Bitstream refers to a mode on your media player where the internal audio processing of the player is bypassed and the audio signals are then sent to an audio processor be it on the TV, soundbar, integrated, preamp, or receiver where the signals are decoded.

The signals are transmitted in a series of 1s and 0s digital bits using digital cables that include HDMI, Coaxial and Digital optical or even wirelessly.

Once the digital bits are received by the audio processor, audio post-processing is done according to the information that is in these bits. The digital signals are then converted to analog signals before transmission to the amp and the speakers.

These digital bits can be stored in various formats that include Dolby Digital, TrueHD, DTS, DTS-X, DTS-ES, Plus, and so on.

It is worth noting that technically the digital bits in the media source files are encoded in almost similar ways in both PCM and Bitstream.

What is Bitstream (re-encode)

Bitstream (re-encode) is more like a hybrid between a Bitstream and PCM output. The Bitstream (re-encode) output works great with older receivers/processors/preamps that do not have an HDMI input port.

Bitstream (re-encode) works like PCM in that the media player decodes the audio file from the source to PCM and it is then re-encoded to compressed formats such as Dolby Digital (DD) or DTS. The compressed high-bitrate signals are then transmitted to the receiver/pre/pro/integrated amp trough an optical cable where it can then be processed/decoded.

This saves you from having to buy an entirely new sound system but you still enjoy the upgraded Blu-ray formats.

Pros and cons of Bitstream

Pros:

  • Less strain is put on the media player.
  • Can send more surround sound channel signals up to 5.1 over coaxial or optical cables.
  • You can take advantage of the superior audio decoding on your receiver.

Cons:

  • Limited secondary audio quality.
  • More strain is put on your receiver.
  • Will need a high-quality AVR/pre/pro for the best results.

When is PCM or Bitstream convenient for your home theater?

When to use PCM

  • For a delay-free audio experience.
  • To get high-res secondary audio which includes PIP commentary, supplementary soundtracks, and descriptive audio.
  • If your AVR/pre/pro does not have a high-quality audio processor.

When to use Bitstream

  • For a 5.1 channel surround sound when using coaxial or optical cables.
  • If your AVR/pre/pro has a high-quality audio processor.
  • To get the processing strain off your media player.

Final verdict

When it comes to Bitstream vs PCM, it generally does not matter because the audio signals will need to be decoded either way. This means that with each, there is no notable difference in audio quality.

However, the only time you will notice a difference is if your media player has a better audio processor than your receiver or vice versa. In this case, you should listen to both to determine which one sounds more pleasing.

The port selection on your devices can also be a limiting factor in which of the two settings to use as we talked about earlier. If your receiver does not have an HDMI port, you may want to use Bitstream for surround sound. This is because optical and coaxial are limited to 2.1 channels in PCM.

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