Techniques to lower bitrate of samples.

Just to be clear, I'm sampling from vinyl and using an MPC2000 classic, so there's no resampling. I would post in the 2000 forums but I thought it'll be better here, as I'm not asking for advice on the 2000, but for advice, that doesn't include resampling.

From what I've gathered after a couple Google searches, I can do one of the two, for THE EFFECT of a lower bitrate (None of these technically lower it, right?)

1. Sample at 45 or 78 rpm (if possible) and then pitch it down in the MPC.

2. (Only really applicable on drums.) Sample the sounds hot.

Are there any more techniques I could use?

There are two things that fundamentally influence the recorded sound. The first is bit depth, or how many samples represent the state of the sound at a given time. The other is frequency, or how often you sample the state of the sound. Bitrate is effectively how many bits are used to represent a sound over a given period of time. Since you can change this value by influencing either bit depth or bit rate, it makes it a bit harder to know which effect you are looking for.

You can effectively reduce the frequency rate of the sample by increasing the pitch of audio, recording it, and then playing it back at a lower audio rate. This will likely have the most dramatic impact on your sound, but it depends on how much the sampler manages anti-aliasing and all that.

Overdriving audio to make it sound "hot" is not the same thing as bit depth reduction. Overdriving has a lot of interesting characteristics that the analogue process of sampling can manifest that don't exist once you've done bit depth reduction.

Definitely take some time learning about these things, but I'd say use your ear. I'm not sure if there is something specific you're looking for by changing the bit rate of the content, but if you can explain what sound you're looking for, I am sure one of us could help you out.

NearTao wrote:There are two things that fundamentally influence the recorded sound. The first is bit depth, or how many samples represent the state of the sound at a given time. The other is frequency, or how often you sample the state of the sound. Bitrate is effectively how many bits are used to represent a sound over a given period of time. Since you can change this value by influencing either bit depth or bit rate, it makes it a bit harder to know which effect you are looking for.

You can effectively reduce the frequency rate of the sample by increasing the pitch of audio, recording it, and then playing it back at a lower audio rate. This will likely have the most dramatic impact on your sound, but it depends on how much the sampler manages anti-aliasing and all that.

Overdriving audio to make it sound "hot" is not the same thing as bit depth reduction. Overdriving has a lot of interesting characteristics that the analogue process of sampling can manifest that don't exist once you've done bit depth reduction.

Definitely take some time learning about these things, but I'd say use your ear. I'm not sure if there is something specific you're looking for by changing the bit rate of the content, but if you can explain what sound you're looking for, I am sure one of us could help you out.

Damn thanks for the comprehensive response. I was mostly just interested in the techniques there are in general, apart from slowing and then speeding up the sample.

Do you have an audio sample or example, of the sound you're looking for?

CharlesRandolph wrote:Do you have an audio sample or example, of the sound you're looking for?

I'm not after a specific sound. Just curious as to what other ways there are to lower bitrate or give the effect of a lower bitrate.

Scrawny wrote:I'm not after a specific sound. Just curious as to what other ways there are to lower bitrate or give the effect of a lower bitrate.

You want to lower bitrate? Just take your original audio and convert to MP3 with lower bitrate.

Scrawny wrote:Just to be clear, I'm sampling from vinyl and using an MPC2000 classic, so there's no resampling. I would post in the 2000 forums but I thought it'll be better here, as I'm not asking for advice on the 2000, but for advice, that doesn't include resampling.

From what I've gathered after a couple Google searches, I can do one of the two, for THE EFFECT of a lower bitrate (None of these technically lower it, right?)

1. Sample at 45 or 78 rpm (if possible) and then pitch it down in the MPC.

2. (Only really applicable on drums.) Sample the sounds hot.

Are there any more techniques I could use?

What you're talking about here is

1. Pitching up/down the sample to add artifacts.

2. Pushing the inputs into the red to add Distortion/Overdrive to sounds. Works well in
Analog, however in digital it's not so nice.

You can achieve a similar sound using EQ, HP/LP filters, and compression effects or you could use an overdrive effects pedal. However, none of this actually changes the bit rate.

There is the plugin route. If you are using MPC Software, you can coax some magic out of both the Resampler & Decimator. Subtle to crunchzilla, however you like. I find they sound amazing if you add back some highs around 14k with either NI's Enhanced EQ or any Pultec style eq. Then there's the NI Crunch Pack, specifically the Bite plugin. Then there's the RC-20. It packs useful extras as well. I use those 4 and my ears per-project. A lot of people like Decimort, I don't care for it. None of these ways are truly "authentic" but can easily add some tasetful crunch.

Bit rate is not bit depth. Bitrate means how much data in a specified time therefor it's stated with bits per second or kilobits per second. Its a value not really used in this context.

A hint to understand bitdeph is to think about a ladder that represents volume. On top of the ladder all 16 bits are set to 1 and this represent 0dBFS (FS means full scale and show that we're talking about digital dBs). Goin down one step on the ladder you're standing on 15bit or in dB -6dB cause 1bit =6dB.
With each step down you pass -6dB so when you reach the bottom of the 16bit/step ladder you're at -96dB. You can't go further it's just mud there which is called noisefloor
What you can do is use a 24bit/step ladder. Then you can reach the -144dB mark.

What does it mean? The more bits an audio interface provide the quiter the audio can be. Recording a very quiet audio signal with a very low bitdepth and then raising the volume (normalizing) after recording/sampling will result in audible noise cause you don't just raise the recorded signal but also the 'mud'.


Also.....(I hope I'm not telling BS with this but thats how I understand it)....more bits mean finer 'inbetween' dB values per step.
On a 16bit ladder the values from -96dB to -90dB are represented by just 1bit which can have 2 states (0 and 1). The values -89.9998dB to -84dB are represented by 2bits (which are 4 states 00, 01, 10, 11) therefor 6dB are divided in 4 parts. Goin up the ladder the states which represent 6dB increase and at the top at 16bit the 6dB are divided in 65535 parts.
I hope this is understandable and my thoughts are correct. Maybe this chart help





Sound examples (this is created in Audition with original 16bit samples so its not true n-bit recording but calculated)
This is the list
16bit
12bit
12bit with dither
10bit
10bit with dither
8bit
8bit with dither
8bit with dither (noiseshaped)
4bit
4bit with dither
4bit with dither (noiseshaped)


Old game music (chiptunes) is also low bitdepth.


The other important value is the samplerate but I'm tired now.....

peace

Scrawny wrote:
I'm not after a specific sound. Just curious as to what other ways there are to lower bitrate or give the effect of a lower bitrate.

Run the signal thru a hard limiter to cut the peaks a bit and then sample this signal at very low recgain. Then normalize the recorded sample.
Recording at very low recgain = using less bits of the converter. Not really the same as if you use an original low bit converter but its a way to get in touch with the noisefloor

peace

Exactly, bit rate and bit depth are not the same.

CharlesRandolph wrote:

Scrawny wrote:I'm not after a specific sound. Just curious as to what other ways there are to lower bitrate or give the effect of a lower bitrate.

You want to lower bitrate? Just take your original audio and convert to MP3 with lower bitrate.

I'm only using my MPC and a junky DJ mixer.

sample hot, try overdriving the record gain knob and keep trying over and over while adjusting it so you can see how it sounds after each recording is done... what you are hearing live is not what the sample will sound like once it is recorded. once you get the sweet spot for that, then re-record the sample at 45 rpm.

it just get an old stereo tape deck and bounce sample back and forth a bunch of times.. try overdriving the signal into the tape deck. Tape decks are 10 bucks on facebook marketplace or goodwill

Sounds like you want to make your sounds inside the MPC but there's other ways, as suggested. It's a fun thing. There are a bunch of different bitcrusher type guitar pedals. Dunno if they're digital or what.
I once recorded vocals with the mike in an old rotary phone. Mom was pissed I took the phone apart but it had the sound I was going for. The band Flipper was genius at taking lo-fi down to the basement.